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Table of Contents
Linux Database Bible ..........................................................................................................................................1 Preface..................................................................................................................................................................4 The Importance of This Book.................................................................................................................4 Getting Started........................................................................................................................................4 Icons in This Book..................................................................................................................................5 How This Book Is Organized.................................................................................................................5 Part ILinux and Databases ................................................................................................................5 Part IIInstallation and Configuration ................................................................................................5 Part IIIInteraction and Usage...........................................................................................................5 Part IVProgramming Applications...................................................................................................6 Part VAdministrivia.........................................................................................................................6 How to Use This Book ............................................................................................................................6 Additional Information...........................................................................................................................6 Acknowledgments ...................................................................................................................................6 Part I: Linux And Databases............................................................................................................................8 Chapter 1: Introduction And Background......................................................................................................9 Origins of Linux ......................................................................................................................................9 Whirlwind adolescence....................................................................................................................9 The future.......................................................................................................................................11 Some Established Linux Distributions.................................................................................................12 Slackware Linux.............................................................................................................................12 Debian GNU/Linux........................................................................................................................13 Introduction to Databases.....................................................................................................................13 History of databases on Linux........................................................................................................14 Introduction to Linux databases.....................................................................................................17 Summary...............................................................................................................................................18 Chapter 2: The Relational Model...................................................................................................................19 What Is a Database?..............................................................................................................................19 What are data?................................................................................................................................19 What does it mean to maintain a body of data?.............................................................................22 Relationality...................................................................................................................................24 The Relational Model...........................................................................................................................24 What is the relational model?.........................................................................................................25 Structure of the relational model....................................................................................................25 Relational algebra and relational calculus......................................................................................31 Relational integrity.........................................................................................................................41 Hierarchic and Network Databases .......................................................................................................46 The hierarchic database..................................................................................................................46 The network database.....................................................................................................................47 Object Databases ...................................................................................................................................47 The impedance mismatch problem .................................................................................................48 Storing objects as they are programmed........................................................................................48 The object−relational compromise.................................................................................................50 Choosing a Type of Database...............................................................................................................50 Application Architectures.....................................................................................................................51 Client−server..................................................................................................................................51 i

CONSEQUENTIAL. She has worked as a technical editor and writer. please contact Copyright Clearance Center. AND THE ADVICE AND STRATEGIES CONTAINED HEREIN MAY NOT BE SUITABLE FOR EVERY INDIVIDUAL. INCIDENTAL. MA 01923. Susan Moritz Proofreading and Indexing: TECHBOOKS Production Services About the Authors Michele Petrovsky holds a Master of Science in Computer and Information Science from the University of Pittsburgh. Trademarks: Linux is a registered trademark or trademark of Linus Torvalds. Nova Scotia. personal. Colleen Totz Project Coordinator: Dale White Graphics and Production Specialists: Joyce Haughey. NEITHER THE PUBLISHER NOR AUTHOR SHALL BE LIABLE FOR ANY LOSS OF PROFIT OR ANY OTHER COMMERCIAL DAMAGES. and has taught at the community college and university levels. and at Gwynedd−Mercy College in 2
. Danvers. THE ACCURACY AND COMPLETENESS OF THE INFORMATION PROVIDED HEREIN AND THE OPINIONS STATED HEREIN ARE NOT GUARANTEED OR WARRANTED TO PRODUCE ANY PARTICULAR RESULTS. Inc. Credits Contributing Author: Fred Butzen Acquisitions Editors: Debra Williams Cauley Terri Varveris Project Editors: Barbra Guerra Amanda Munz Eric Newman Technical Editor: Kurt Wall Copy Editor: Richard Adin Editorial Managers: Ami Sullivan. INCLUDING BUT NOT LIMITED TO SPECIAL. LIMIT OF LIABILITY/DISCLAIMER OF WARRANTY: THE PUBLISHER AND AUTHOR HAVE USED THEIR BEST EFFORTS IN PREPARING THIS BOOK. OR OTHER DAMAGES. published several books on a variety of computing topics. or educational use. NO WARRANTY MAY BE CREATED OR EXTENDED BY SALES REPRESENTATIVES OR WRITTEN SALES MATERIALS. THERE ARE NO WARRANTIES WHICH EXTEND BEYOND THE DESCRIPTIONS CONTAINED IN THIS PARAGRAPH. Hungry Minds. THE PUBLISHER AND AUTHOR MAKE NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS BOOK AND SPECIFICALLY DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. or fax 978−750−4470. Brian Torwelle. Michele has administered UNIX and Linux systems and networks and has programmed at the application level in everything from C to 4GLs. All other trademarks are property of their respective owners.For authorization to photocopy items for corporate. is not associated with any product or vendor mentioned in this book. 222 Rosewood Drive. most recently at Mount Saint Vincent University in Halifax. Jacque Schneider. Erin Zeltner Quality Control Technician: John Greenough.

he has worked strictly in the software field. he worked in both commercial and government electronic hardware development and manufacturing. In 1998. Since 1990.
3
. primarily in database systems.southeast Pennsylvania. He uses his Linux box as the primary development tool for very large database applications. At Los Alamos. Until 1990. Steve holds a Master of Science in Computer Engineering from Pennsylvania State University. Mojo moved into the private sector to work for a small data warehousing company. Stephen Wysham has been working in the electronics and software industries since 1973. Mojo Nichols began working on UNIX systems at Los Alamos National Laboratory in 1992. Mojo helped develop large image archives using primarily free software.

or you have an interest in the applications that are possible on Linux.Preface
Welcome to the Linux Database Bible. you should have successfully installed Linux. This would not have been possible without the availability on Linux of capable relational database management systems (RBDMS) that made it easier to support surprisingly robust database applications. In some cases.
The Importance of This Book
Through the past several years. By reading and applying what this book contains. you will become familiar and productive with the databases that run on Linux. A database that includes PHP or has Perl DBI support is desirable. The growth of Linux has been due in no small part to the applications that were readily available or easily ported to it in the Web application space. but this book deals with Linux database application development from a broader perspective. Quite a few advanced Linux books are available. If your job involves developing database applications or administering databases. with more than a few of them available under Open Source licensing. to name two examples. Linux use and acceptance has been growing rapidly. Now is definitely an excitingand potentially rewardingtime to be working with and deploying Linux database solutions. Any system that can run Linux will suffice. • A copy of Linux that is compatible with the version of data that you have chosen. The number of Linux databases is somewhat astounding when you consider them all. such as MySQL. To make the best use of this book. Linux lends itself to database development and deployment without the overhead of the proprietary UNIX ports and is a prime way to get much of the same flexibility without the same magnitude of cost. Those that are thriving are serious contenders for many applications that have had to suffer through the shortcomings of the Microsoft Windows architecture and application paradigm. Most of the Open Source databases and database−integrated applications are installed in a more or less similar way. you should be using at least 4
. • A programming language that is compatible with both Linux and the database that youve chosen. others are gaining features regularly. you will need: • A copy of one of the Open Source databases for Linux. Linux database development is a deep and fertile area of development. These are freely downloadable from the Web. then this is the book for you. such as C/C++ or Perl. Some have already fallen by the wayside. There are numerous Internet sites from which you can download Linux.
Getting Started
To get the most out of this book. Experience shows that early adopters of a new paradigm tend to be already technically proficient or driven to become the first expert in their circle of influence. youll have to make choices in the installation that have some effect further down the roadfor example installing the Apache Web Server and having to choose which CGI program to load or installing MySQL with or without built−in PHP support. but youll be much better off with a fast Pentium−based machine with loads of memory (even though Linux can run in small memory spaces. During this same period several dedicated groups have been porting existing RDBMS to Linux.

How This Book Is Organized
This book is organized into five parts: introduction to Linux database with some background on relational databases.32MB of RAM). Caution We want you to be ready for potential pitfalls and hazards that weve experienced firsthand. Even the application programming will be done in text mode windows.
Note A point of interest or piece of information that gives you more understanding about the topic at hand is found next to this icon. the plentiful Linux support applications can take up a significant amount of disk space. We also provide a detailed background on the development and importance of SQL and help you understand the process of building a database system. And a mouse please dont forget the mouse. and PostgreSQL. Cross Reference Youll find additional informationeither elsewhere in this book or in another sourcenoted with this icon. Also. At any rate. the display resolution is pretty much moot. 5
. you should be using at least a 1−GB disk to begin with. Youll find detailed discussions of specific products and steps to follow in the process. We wrap up Part I with chapters on determining your own database requirements and choosing the right product to meet your needs.
Icons in This Book
Take a minute to skim this section and learn what the icons mean that are used throughout this book. MySQL. This icon alerts you to those. In addition to basic operation and navigation. for the typical Linux desktop you should have at least a 600x800 pixel resolution video board and display. In this Part we introduce relational databases along with some relational database theory and discuss object databases briefly. However.
Part IIInstallation and Configuration
Installation and configuration of database products are covered indepth in Part II. In these cases. Tip Heres our opportunity to give you pointers. and dont forget the size of the database that you plan on creating. programming applications. and general database administration. this Part shows you what vendor−supplied tools can help you accomplish. installation of a Linux database. How about video board and display? Many of the Linux databases use a command line (that is. text) interface (CLI).
Part IIIInteraction and Usage
The two chapters that make up Part III of this book delve into ways the Linux database administrator interacts with the database and provide detailed information about tools available to the DBA. interacting with and using an database. In addition to a brief history of Linux.
Part ILinux and Databases
Part I introduces you to Linux and provides background about development and history. referring specifically to Oracle8i. youll find background on databases in general and databases as they pertain to Linux. Youll find suggestions and the best of our good ideas next to this icon.

Steve Wysham I would like to acknowledge Deborah Kline for her help in editing and writing and Tim Thomas for his reasonable and invaluable advice on how to proceed.
Additional Information
In addition to the URLs presented throughout this book. as well as telling you how to prevent disastrous breaches.com/development/index. you may try the index first to see which section in the book specifically addresses your problem. you are more than welcome to. I would also like to thank Mojo B.com (access to a wealth of Oracle documentation)
Acknowledgments
Both the quality of the work of the Open Source community. the Perl DBI API. we recommend that you consult any of the following for further information on the Linux DBMSs we discuss: • http://postgresql. PHP (and MySQL).mysql. folks. "the geeks behind MySQL" and "whats planned for future releases") • http://otn. managing various processes.com/devel−corner/index. picking up useful tidbits here and there. 6
. And lastly. We discuss backing up your system. but Im not sure just for what. Often the chapter order is immaterial.
Part VAdministrivia
Part V has an odd−sounding title that simply means administration details that a Linux DBA would need to know.html (the entry−point to all online MySQL documentation) • http://www. Michele Petrovsky I would like to thank Mary Kay Wysham for her patience while I typed just a few more things. and dealing with intermittent tasks.readysetnet. If youre faced with a challenging task. the Java JDBC API. Command line client tools and some performance issues are also included. Nichols. for a job well done.oracle. as the site puts it. We also present standalone database applications and illustrate how one such application might be specified and implemented. Congratulations.html (information about.com/documentation/index.mysql.
How to Use This Book
You can use this book any way you please.html (the PostgreSQL Developers Corner) • http://www. If you choose to read it cover to cover.Part IVProgramming Applications
Part IV reviews and introduces several database Applications Programming Interfaces (API): the ODBC API with C/C++. we wrap up with a discussion of modern database deployments and a look at the future. We walk you through the process of building a database application using PHP and MySQL and updating a database from a Web page. Weve included important information about security and creating a security policy surrounding your database. We suspect that most readers will skip around. and the dedication of the members of that community to their work and the sustaining ideals deserve to be acknowledged. as exemplified in this book in the discussions of MySQL and PostgreSQL.

There is no single reason why so many contributors were drawn to the Linux project. a UNIX clone for Intel processors that was popular in universities.org for more information.os. people often refer to Linux as the combination of the Linux kernel and a large collection of software that has been written or rewritten to operate with the Linux kernel. either commercial or volunteer.
Origins of Linux
Linus Torvalds wrote the Linux kernel. a collection of free software ranging from compilers to text editors. version 5.0 of the Linux kernel was released in 1994. including Alpha. Caution Open source is a term that has been knocked about the press quite a bit lately. or purchased by CD−ROM.Chapter 1: Introduction And Background
Linux is an open source operating system modeled on UNIX. The project grew steadily in interest among hard−core UNIX hackers and operating systems enthusiasts. Throughout the 1990s. you need to comply with the requirements of SPI and/or OSI. PowerPC. grew dissatisfied with Minix. In 1991. a not−for−profit organization. Torvalds posted a now famous message to the Usenet newsgroup comp. Many companies. If you desire to designate your product as Open Source. It emerged as a hobbyist favorite over such similar efforts as FreeBSD. as well as a process for validating software licenses as open source. version 1. Linux refers to the kernel of the operating system. it had been considered a momentous event when Digital Equipment Corp. gather the Linux kernel and some selection of Linux software into distributions that can be downloaded over the Internet. the opening of a well−known product such as Netscape brought a lot of attention to the open source community and to Linux. which was shaping up to be its key success story.0. Torvalds. reaching approximately a half million Linux users. A second reason was Torvalds knowledge. Please see www.opensource. leadership skills. PA−RISC. ranging from improving Linuxs hard−drive compatibility and performance to support for IBM PC sound cards. It also marked a key turning point in the perception of such free software by admitting the validity of commercial interests in open source. It was ported to many platforms. ARM. In no particular order:
9
. and very soon began to attract attention from businesses. Many other events shaped Linuxs spectacular growth in 1998. Linux was gaining a great deal of momentum. including many developments in the Linux community. While many in the press and big business had little need to think about operating−system kernels. Linux gained in popularity. 68000. Informally. then a student at Helsinki University. Regardless of the reason. but after the frenzy of excitement over Mozilla. Some contributors were drawn to the project because all contributors were given the right to copyright their contribution. In 1997. Eric Raymond presented his paper. big−business interest in Linux became routine. which was instrumental in publicizing and providing the background for open source software in general. which was nicknamed Mozilla. officially sanctioned the Alpha port of Linux. and SPARC. which manages system resources and running programs. Many of these tools are part of the GNU project. The Cathedral and the Bazaar. Linux immediately attracted several key contributors in all areas. Technically. but it is important to note that it is a trademark of Software in the Public Interest (SPI). in many cases. Both Open Source Initiative (OSI) and SPI have specific definitions of open source. and personality.
Whirlwind adolescence
In 1997. this paper influenced Netscapes 1998 decision to initiate an open source effort to develop the next major version of Netscape.minix asking for help and asking about interest in a UNIX−like operating system he planned to write for Intel 386 and higher processors. As such.

including an appearance on the cover of Forbes. a larger number of users and groups. Oracle. enabling operations to be distributed to multiple machines for faster processing. Even with all the media and business attention paid to Linux in 1998. which seemingly signaled Microsofts war cry against the upstart Linux. among other features and improvements. an improved scheduler to handle more processes. announced ports of their main database management systems to Linux. to compare Linux and Windows NT. two prominent organizations in the Linux and open source community. • The major market research companies began to report on Linux usage and quality. Red Hat defied many observers expectations. fought over trademark of the term open source. 1999 was the year of Linux. a high−quality open source application that is similar to Photoshop and that was developed on Linux. The 2. • In yet another sign of the internal strife that fame and fortune can bring. • In an extraordinary gesture. but had done no more than post an obscure newsgroup message on the Linux end. Red Hat. and improved device support. • Red Hat. They are groups of low−cost Linux machines. • A venture capitalist actually encouraged one of its interests. OSI and SPI. gaining dramatic value in a 10
. Informix. On the positive front. erstwhile presidential candidate and perennial libertarian gadfly petitioned PC hardware vendors to preinstall non−Microsoft operating systems on their machines. • Most relevant for this book. after offering IPO shares to various open source contributors. but controversy erupted when it became known that Mindcraft had obtained extensive tuning data for NT. SuSE. along with some not−so−internal responses after the fact. including hiring Mindcraft Inc. it was alleged that Mindcraft had conducted unfair comparisons against Novells Netware to discredit that operating system. The current version. that are connected with Ethernet networks. announced that it would incorporate the popular open source Web server Apache into its WebSphere application server. including IBM. and Sybase. Inc. up to 140 in the case of the Avalon cluster at Los Alamos National Laboratory. • Several organizations launched efforts to standardize aspects of Linux distributions. and many arguments on whether it spelled the end of proprietary operating systems such as Microsoft Windows NT occurred.4. removes (prior) PCI bus limits. as well as a few smaller players began to put increased effort in promoting their existing commercial support for Linux. • GIMP 1. Beowulf clusters were developed by Linux users at NASA and elsewhere. proving Linuxs extraordinary strength in distributed computing.• It became publicly known that some scenes from the blockbuster movie Titanic were rendered with groups of Alpha−based machines running Linux. The study showed NT at a definite advantage. commercial database vendors. was released. Ralph Nader. supports up to 64GB of physical RAM and unlimited virtual memory. Digital Creations LLC. particularly Linux. leading to much publicity in the trade press.0. 2. and that Microsoft had the authority to forbid the publication of sponsored results. and immediately showed impressive performance. which removed one of its greatest weakness in the eyes of businessesthe perceived lack of formal technical support. Linus Torvalds appeared in prominent interviews and features in mainstream newspapers and magazines. besides making very positive noises about support for Linux. and Caldera. but excluding Microsoft. Also. • Internal documents from Microsoft were leaked to Eric Raymond. The marketplaces perception of Linux matured as smoothly as did Linuxs technical component. The quality and popularity of GIMP proved that open source desktop applications on Linux are as viable as Linux servers have proven to be. • Several supercomputers based on Beowulf clusters went online. becoming. Microsoft has begun its inevitable counterattack. and announced software projects aimed at contributing back to the open source community. went public. the infamous Halloween Papers. of the Linux kernel was developed and released under intense media scrutiny.4 kernel provides improved multiprocessor support. • IBM. to release its flagship application server Zope as an open source product.

a key library that underlies the vast majority of Linux products. As its pioneers become netrepreneurs and celebrities. and so on) divert or divide the effort that is currently going into free software? Will slick Linux products from companies with large research and development and user−interface design budgets kill the interest in open source alternatives? Considering that Linux and its sibling projects flourished so well in a software industry in which openness had long appeared to be a distant dream. or on pages downloaded from the Web. a fruitful symbiosis is possible between the suits and the hackers. the most common file system for Linux has a file−size limit of 2GB on 32−bit systems. the amount of memory that Linux can address will be increased. The biggest question is what transformations this growth will impose on the community and technology. the real test of Linuxs 64−bit prowess will come as Intels next−generation IA−64 microprocessor. The 64−bit move will have many benefits. one wonders whether the circus will impede the tremendous productivity that has been displayed by the open source community.market that appeared to have soured on many recent stock offerings. Note that this bug will also affect other 32−bit non−UNIX systems. the most pervasive license in Linux distributions.k. There is little question that Linux will be out of the gate early for IA−64. There is a 64−bit Linux for Ultra−Sparc and DEC. 1901. licenses have an extraordinary amount of political and philosophical bearing. TCL. and has enough unorthodox provisions to make such a test a lively one. Merced. make an effort to set standards for licenses of included software. Additionally. has never been tested in court. there is much on the way for Linux. sendmail.a. a danger that cannot be discounted and that has prompted much consideration in Linux discussion groups. 1999 was the year in which many application−server and middleware companies followed the major databases into the Linux market. Whatever happens. The General Public License (GPL). Intel has also pledged to provide early samples of IA−64 servers to key companies to bootstrap the porting of open source projects to the platform. should be headed off. which could well ensure that Linux is the first OS ported to this long−awaited platform. which emphasize providing the source code of software. has been updated to ensure a smooth transition to 64−bit. usually on the Intel platform. Ext2. Some distributors. In the Halloween Papers. Most Linux users are advocates of open source licenses. The Linux kernel is distributed under the Free Software Foundations General Public License (GPL). Note Licenses are not the same as copyright. In the Linux community. is released and becomes popular in servers and among power users. Also. which will be vastly raised by the move to 64−bit. and glibc. On a technical level. a. and the open software community in general. 2038. Free software purists also question the result of Linuxs increasing commercialization. A group of commercial interests known as the Trillian project is committed to porting Linux to Intels upcoming IA−64. Most of the obstacles to Linuxs success in the world of enterprise information systems and terabyte databases are being addressed. Many software users are accustomed to blindly accepting software licensing terms as encountered on software packaging. so that end users do not need to worry 11
. Nevertheless. its unlikely to be dull watching Linux march into the next century. such as Red Hat. Microsoft raised the potential of attacking the open source community with software patents. One major expected move in the next several years is to 64−bit architectures. whether free or paid for. and allowing the end user to make their own modifications to such source code as needed. is December 13. There are open legal questions.
The future
Linuxs continued growth appears unstoppable. several of which are pertinent to database users. The vast majority of Linux systems are 32−bit. and the Y2038 bug. but many of the software additions added by distributors have different licenses. The Y2038 bug is caused by the way 32−bit UNIX libraries store time values. and as political battles take attention from the software. which would make affected systems think that January 19. Will large corporations merely harvest the hard work of open source developers without contributing anything? Will all the open source projects going corporate (Apache.

com. and Canada.
12
. In 1998. rich technology. Additional information about SuSE can be found at www. excellent documentation. a software company. SuSE Linux is the international technology leader and solutions provider in open source operating system (OS) software. is a leader in providing Linux−based business solutions through its award−winning OpenLinux line of products and services. Red Hat is the leader in development.0 include thousands of third−party Linux applications supported by extensive professional consulting and support services. Inc. Its award−winning SuSE Linux 6. Inc. France. California. MandrakeSoft has facilities in the United States. are privately held companies focused entirely on supporting the Linux community. Caldera Systems. Inc.com site and the MandrakeExpert. operating systems. and Internet technologies that are based on pioneering work done at the Computer Systems Research Group (CSRG) at the University of California at Berkeley. headquartered in Germany. Red Hat is the principle provider of GNU−based developer tools and support solutions for a variety of embedded processors. Inc. and soon to be iXsystems) sells BSD Internet Server systems. Caldera International. and Linux kernel expertise. BSD technology is known for its powerful. and the GNU General Public License. Open Source development. is planned combining the assets of Caldera Systems with the assets acquired from SCO. effective configuration and intelligent design result in the most complete Linux solution available today.suse. setting new standards for quality and ease of use. and portable architecture. based in Oakland. and an encyclopedic set of Linux tools. The shareholders of SCO (nee Santa Cruz Operation) have approved the purchase by Caldera Systems. of the both the Server Software Division and the Professional Services Division of SCO. and SuSE Inc. and for its advanced development environments.. and the knowledge of its computer scientists to its customers. and management of Linux and open source solutions for Internet infrastructure ranging from small embedded devices to high−availability clusters and secure Web servers. MandrakeSoft. comprehensive hardware support. Inc. SuSE Linux AG. Leading CSRG computer scientists founded BSDi in 1991. Founded in 1992. Caldera Systems. was founded in 1994 by Ransom Love and Bryan Sparks.K. BSDi offers strong products.about such issues as much. deployment.
Some Established Linux Distributions
Founded in 1994. Based in Orem. In addition to the award−winning Red Hat Linux server operating system. developer tools. BSDi is recognized for its strength and reliability in demanding network−computing environments. Utah. Caldera.
Slackware Linux
Slackware (a trademark of Walnut Creek CD−ROM Collections) is itself a part of BSDi. Today. is the official producer and publisher of the Linux−Mandrake distribution. SuSEs distribution. flexible. was created to develop Linux−based business solutions. surrounding features. BSDi (nee Berkeley Software Design. Designed for Web and enterprise server environments and efficient as a home and office platform.4 and the newly released 7. A new company. and smaller and medium sized organizations a set of GNU Linux and other Open Source software and related services.. MandrakeSoft provides small office. MandrakeSoft provides a way for (Open Source) developers and technologists a way to offer their services via the MandrakeCampus. and offers support and engineering services to organizations in all embedded and Linux markets. home office.. networking. and are free to modify and redistribute code as needed. Germany. Inc. (Nasdaq−CALD). Red Hat provides runtime solutions. the U.com site.

For instance. E.Debian GNU/Linux
Debian was begun in August 1993 by Ian Murdock. FL
13
. As a side note.
Introduction to Databases
A database is merely a collection of data organized in some manner in a computer system. in which the columns set formal boundaries of the type and some rules for the different bits of information that combine to form a coherent entity. payroll and demographic information for such employees. For instance. For example. J. as a new distribution that would be made openly. Originally. well−organized community of developers and users.org) and IRC (#debian channel at irc. but the columns make sure that the set of information in each row is consistent. Date. relational databases organize data into groups known as tables. Codds theoretical work was expounded on by C. published in the early 1980s. The strength of relational databases lies in providing a methodology for expressing relationships between tables.debian. a relational database would prevent a user from trying to set Carla Wongs age to a string value. or in more complex form it might incorporate all the organizational. In particular. Communication is done primarily through e−mail (mailing lists at lists. and to be maintained and supported with similar care. This much could be achieved using flat−file databases. In practice. Codd developed the seminal work on the theory of relational databases in the late 1960s. It started as a small. F. Codd is also known for his twelve criteria for an On−Line Transaction Processing (OLTP)−compliant database. Few of the developers have actually met in person. two that have not are network databases and hierarchical databases. consider the following representation of the information in Table 1−1 (Employee Table):
Table 1−1: Employee Table Employee ID Name Age Department 101 Manny Vegas 42 12 102 Carla Wong 36 15 103 Arnold Page 38 15 Each row of data describes a distinct abstract entity. in the spirit of Linux and GNU. you could speed up applications and improve the value you can get from your databases. for instance. one theory that has remained dominant is that of relational databases. Some people use the term strictly to refer such collections hosted in nonvolatile storage. A database could be as simple as a list of employee names in your department. tightly knit group of free software hackers and gradually grew to become a large.debian. we could have another data representation. but some people consider organized data within memory a database. Roughly 500 volunteer developers from around the world produce debian in their spare time. on hard disk or tape.org). Debian was meant to be carefully and conscientiously put together. but in the 1970s much academic and industry research showed that if you organized the data in certain ways. as shown in Table 1−2:
Table 1−2: Department Table Department ID 12 Department Name Accounting Location Miami. most databases were just lists of such data in an ASCII file.

by the appropriately named Revolutionary Software. provided no technical support for the Linux version. It took the approach. you would have an orderly way of determining where Carla Wong was located by reading her Department value from the first table. one might have an order table related by a foreign key to a customer table. supporting platforms from MacOS to Mainframes. POET software did not port future versions of their DBMS to Linux until 1999.
14
. Just Logic Technologies Inc. These differ from traditional relational databases in that the relation between tables is replaced by using inheritance. Relational database theory provides rules for keeping such relationships consistent. so that the UNIX−savvy could write entire RDBMS applications in shell script. a DBMS and applications development system from the xBASE/Clipper/FoxPro mold.99 version of the Linux kernel. a formal relational calculus details the strict deterministic behavior of relational databases. and OS/2. began experimenting with Linux in departmental systems. Vectorsoft Gesellschaft fuer Datentechnik mbH released CONZEPT 16.1 to Linux. a full−featured client/server SQL DBMS with cross−platform compatibility with other UNIX systems.
History of databases on Linux
Soon after Linux started showing its strengths in portability and stability. YARD Software GmbH released YARD SQL. an SQL RDBMS with a Motif query interface. /rdb consisted of over 120 such commands. a pioneer of object−oriented DBMSs. For example. This is somewhat analogous to the approach of MH among UNIX e−mail user agent software as opposed to such integrated executables as Pine. At its most abstract level. a few vendors in the ferociously competitive database market looked to gain a small competitive advantage by porting to the budding operating system. released Just Logic/SQL for Linux. in a RDBMS. was /rdb. a few pioneer businesses. Flagship at first even supported the 0. of dividing all the DBMS management functions into small command−line commands. especially those that had always used UNIX. A relatively recent developmentin terms of commercial availabilityis the Object−Oriented database (or Object Relational DBMS). Unsurprisingly.15 Human Resources Gainesville. POET Software GmbH. in October 1993. embedding the referenced table in the referencing table. however. and maintain databases. that is. Windows. The interesting thing about Flagship is how prolific it is. rather than using C/C++ call−level interfaces (CLI) or 4GL. and for speedy analysis of data even when there are many complex relationships. /rdb is a decidedly odd fish among commercial DBMSs. So. Vectorsoft. which were dominant before SQL took over. Perhaps the first into the breach. a complete application tool−kit with a proprietary RDBMS at its core. An RDBMS is a DBMS specialized for relational data. Several companies introduced DBMS programs in 1994. Multisoft Datentechnik GmbH released Flagship for Linux. A database management system (DBMS) is software to access. The Linux version omitted the graphical database interfaces that were provided on Windows and OS/2 platforms. FL You could establish a formal relationship between the Department field of the first table to an entire row in the second. and following the relationship to the second table where her location is specified. DOS. one would instead have the customer object as an attribute of the order object. ported the Personal edition of POET 2. manage. very popular among UNIX users. This kind of construct obviates the need to explicitly join the two tables in any query. but in an ORDBMS. for instance.

which provided low−level. The RDBMS was free for academic use. Michael Widenius created a SQL RDBMS engine based on mSQL and called MySQL. a simple fact that led to the development of several of the better−known open source databases for Linux today. David Hughes of Bond University in Australia wrote a SQL to PostQUEL translator as a front−end for Postgres. Conetic Software Systems. was independently ported to Linux. He then decided to also add a back−end to the translator creating a full−blown RDBMS. Eventually a series of HOWTO documents emerged for installing Oracle and other such databases under Linux with the iBCS emulator. and Unify/Accell on Linux.. supporting UNIX. and guaranteed portable connectivity across all supported platforms. Infoflex Inc. The year 1995 was another active Linux year. Inc. an experimental academic database from the University of California at Berkeley. Empress Software released Empress RDBMS in personal and network (full−function) packages for Linux. commercial−quality server with SQL support. took note of the general satisfaction enjoyed by such experimenters even though their efforts were not officially supported. Postgres95 provided Linux support. Postgres95 was released as a first milestone in a journey to turn the formerly experimental. Informix. free. Support of SCO UNIX binaries using the iBCS2 emulator in the Linux kernel led to many reports of intrepid users successfully running SCO versions of Oracle (version 7). and VMS platforms. released C/BASE 4GL for Linux. subject to its copyright restrictions. academic Postgres DBMS into a full−blown. soon released its libraries for client application development. 1996. flexibility. PostQUEL is based on QUEL. The database was almost immediately ported to Linux and grew tremendously because of its speed. embedded SQL and 4GL interfaces to query and maintain third−party databases. The following year. DOS. but were unsupported. Sybase. a software development kit for the popular Open Database Connectivity (ODBC) standard. and it can be argued that the maintainers have done a good job of meeting their goals. Postgres used a proprietary query language. Dataflex. saw two additional advances in the world of Linux. which could be compiled on Linux. and a more liberal copyright than most other free databases had. was becoming a useful product. ported to Linux. Some vendors. an RDBMS based on Ingres. UDBC supported many platforms. Empress was one of several commercial databases sold and supported through the ACC Bookstore. which provided an xBASE database engine with a 4GL interface. released a Linux version of its SOLID Server RDBMS. sensing the excitement of its customers who were running its DBMS on Linux under the emulator. particularly Unify. ported its multidimensional database engine to Linux. a product of research at the University of California at Berkeley. which was used in earlier versions of Ingres. They licensed source code to customers. The libraries were available for free on Sybases Web site. called mSQL. It was one of the first major database companies to notice and support Linux. Solid Information Technology Ltd.1. Ingres. Pick Systems Inc. Ingres used the proprietary QUEL query language rather than SQL. OpenLink Software introduced Universal Database Connectivity (UDBC). PostQUEL as its interface. Mostly the work of Andrew Yu and Jolly Chen. (Just Logic/SQL was also sold through ACC). In fact. especially with the recent release of PostgreSQL 7. including Linux. It was soon renamed PostgreSQL. Sybase. released ESQLFlex and Infoflex for Linux. but revived it in 1999.2. Its probably more than mere coincidence that 15
. Pick eventually dropped its Linux version. an early outlet for Linux merchandise.Postgres.

UNIX and Linux are demonstrating their superiority over Microsofts resource−hungry server operating system.5. In scalability. 16
. But 1998 was also a year of advances. so that it could do its own filesystem management rather than relying on the OS. a well−known SQL RDBMS (but not its enterprise−level Dynamic Server). In all these areas. Raima Corporation offered Linux versions of Raima Database Manager++. and offering development versions of these tools for a free registration to the Informix Developer Network. and several indexing methods for data. triggers. as weve already discussed. And this even though there is a Windows NT version of InterBase available! Computer Associates announced that it would be porting their commercial Ingres II RDBMS. see the July 6. Of course. announcing ports of Informix−SE. Coromandel. Inprise Corporation (formerly Borland International) released its Interbase SQL RDBMS for Linux. For proof of just how the porting frenzy of 1988 surprised even the vendors themselves.ehlinux. Oracle.such an early Linux booster among DBMS vendors is a Finnish company.infoworld. from ANSI−SQL 92 support to stored procedures. a specialized client/server database engine geared towards storing and manipulating relationships between text objects. saw Linux as a marketable platform for such systems. which became Oracle8. In 1997. it had facilities for presenting data sets as HTML and a specialized query language. 8i. Informix officially committed itself to Linux. To quote from the paper: UNIX and Linux are better as server platforms than Windows NT. in 1997. was ported to Linux in 1999. bypassing the need for clients to buy Microsoft and other expensive operating systems. Oracle announced a Linux porting effort. 1998. IBM. Of course. made a step towards the raw−iron ambitions by bundling an Internet filesystem to the database. stability. and especially performance. and other Informix components. Oracle8i.com/cgi−bin/displayStory. As such.pl?98076.htm ) reporting that the major DB vendors. Solid announced a promotion giving away free copies of the SOLID Server for Linux users in order to galvanize the development of apps based on SOLID by Linux developers. UNIX and Linux contain more mature and proven technology. which approximated the raw−iron goals. Oracle. from India.0. At one point Oracle even declared its intention to begin distributing Linux as a bundle with its DBMS.5 for Linux. and followed up the release by posting to its Web site a white paper making startling advocacy for InterBase on UNIX and Linux. Empress updated its Linux RDBMS. This ambitious set of products sought to tackle data needs from C/C++ object persistence to full SQL−based relational data stores. security. and Sybase had no plans for releasing Linux ports of their DBMSes. Lastly. adding such features as binary large object (BLOB). Oracles follow−up release to 8. KE Express was also released for most UNIX varieties as well as Windows and Macintosh. At about the same time as Informix. Nevertheless. Informix. 1998 was the year that the major Database vendors took serious notice of the operating system. HTML application interface support. released KE Texpress for Linux. Infoworld article (www. built a lot of high−end features into Integra4. ESQL/C. Then.0. and 4GL tools: features typical in high end SQL RDBMSes. which also featured other improvements such as XML support. which had always been looking for a way to sell raw−iron (the practice of selling the computer without an installed operating system) database servers. KE Software Inc. but it did reveal the prevailing expectations in the industry. it later became known that some of the quoted vendors were actively beta testing their Linux products at the time. Raima Object Manager and the Velocis Database Server. Coromandel Software released Integra4 SQL RDBMS for Linux and promoted it with discounted pricing for Linux users.

by the time they were nearing completion of the port. Sybase announced a port of its enterprise−level adaptive server enterprise (ASE) to Linux.2000 database engine running with SuSE Linux on Compaq Computer Corporations 64−bit Alpha processor for customer shipments.31 for the Linux platform. Informix released Informix Dynamic Server. and Inprise Interbase 5. Informix supports the common (generic) Linux component versions. ADABAS D. In August 2000. In 1998. At about the same time. Linux Edition Suite. One small problem that emerged after all this activity was that most of the major DBMSs that had been ported to Linux had lower or more expensive support costs. but this flexibility is probably not characteristic of the large organizations on which Linux DBMSs were poised to make a debut. an open source SQL query tool for multiple databases. from which Web sites users could download trial versions of the software for free registration. Many of the vendors seemed to be relying on Linux users extraordinary ability for self−support on online forums and knowledge bases. sophisticated network interfaces. Java. including MySQL. These include Oracle8i. and announced Red Brick Decision Server version 6. stored procedures in C. and several released their software only in RPM form. layered and comprehensive security. most enterprise DBMS vendors offer per−CPU pricing. notably PostgreSQL and MySQL. and almost immediately struck agreements with Caldera and Red Hat. Enterprise databases were traditionally licensed by the number of connected users. DB2 announced that it would be porting version 5.1. SuSE.1. which are discussed throughout this book. such as Red Hat. dbMetrix has a GTK interface. and Caldera on Intel platforms. There are several open source databases that support a subset of ANSI SQL−92. DB2 Universal Database 6. serious concerns emerged in the Linux community about the dominance of Red Hat software. the DB2 port was performed by a few Linux enthusiasts within IBM without official approval. saw a PR problem and pledged support for multiple distributions (four in Oracles case.Note As of this writing Oracle9i is about to be released. mSQL. In 1998. mSQL is a similar product to MySQL. Informix. and heavy third−party support. Soon after the major vendors announced their DBMS ports. SQL embedded in C/C++ and Java. Sybase ASE 11. Most of the vendors struck a partnership with Red Hat. but such software is still very 17
. from in−memory DBMSs such as Gadfly (open source) to full−fledged enterprise systems such as Oracle8i. Some. or a variety of proprietary languages. transaction management. Informix Corporation simultaneously introduced a developers edition of its Informix Extended Parallel Server (XPS) Version 8. such pricing became unfeasible because there was no practical limit to the number of users that could connect. Solid. and Oracle. including versions of Linux for the Alpha processor). Luckily. Informix Corporation announced the availability of its Informix Dynamic Server. Storey began developing dbMetrix. In Fall 2000. but with the advent of the Web.0. as well as bundling with SuSE. Interestingly enough. for data warehousing in Web or conventional decision−support environments. the announcements for commercial Linux software were coming along thickly and the developers were able to make a business case for the port and get it sanctioned. Bundling on the distributions application sampler CDs would follow. The major commercial databases tend to have support for full ANSI SQL−92. Many of the vendors involved have since normalized their Linux technical support policies. David E. Both products are the first for Linux designed expressly for data warehousing and decision support. Nowadays. PostgreSQL.2 of its high−end Universal Database Server. like Oracle.
Introduction to Linux databases
A variety of databases run on Linux.

linuxgazette. for example. This has especially been the case in Linux where vendors have tried to seed excitement in the Linux community with the lure of free downloads. It remains to be seen how this will affect the development of the many SQL databases that do not meet the ANSI SQL−92 requirements. There are Web−based. We shall discuss how to determine if Linux database tools are suitable for your needs. although many of them are immature. GTK. Python. which could be as unassuming as a hobbyist Web site with banner ads. query and connectivity tools. It is important to note that the license for these giveaways usually only extends to noncommercial use. which is specialized for organizing bits of object−oriented data for Web publishing. part of Digital Creations Zope application server. There are usually many options for connecting to DBMSs under Linux. Perl.linux. • Linux DBMSs have similarly evolved from the spate of xBASE−class systems available from medium−sized vendors in 1994 and 1995 to the recent porting of all the major enterprise DBMSs to Linux beginning in 1998. is subject to the full licensing fees. C and C++.com. In the next chapter. In this chapter. Commercial OODBMS will be available once POET ports its Object Server to Linux. New Feature There is now a new version of ANSI SQL available. from its creators dream of a modern hobbyists OS in 1991 to the fastest−growing platform for enterprise computer systems in 2000. Tcl/Tk−based. and more than one CGI program has native connectivity to a database.
Summary
This chapter provided some general background about the use of databases in Linux. www. Linux news outlets such as www. such as the great Linux migration of enterprise databases in 1998. you learned that: • DBMSs have evolved greatly as the types of data being managed have grown more complex. POET will support ODMG OQL and the Java binding for ODMG. which is now mainly an Embedded systems database. and KDE SQL query interfaces for most open source and some commercial databases.linux.expensive and usually a significant corporate commitment. and. with OODBMSs and other advancements close around the corner. we shall start the process of sifting through all these possibilities. and specialty DBMS. PHP and MySQL. and www. and how to select the best options if so. As you can see. SQL 99. Many of the vendors offer special free or deeply discounted development or personal versions to encourage third parties to develop tools and applications for their DBMS. Database connectivity is available through several Web servers. the field is constantly evolving and drastic changes can occur almost without warning.com are a good way to keep abreast of all that is happening in these areas. There are libraries for Database connectivity from Java. in the case of commercial databases. such as Empress RDBMS. • Linux has grown phenomenally. but not other aspects of the standard. There are many specialized databases for Linux.
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. • There is currently a wide variety of RDBMS. Any deployment in commercial uses.org. and Zserver.

are part of the wealth of data with which an observer can reconstruct practically every pitch. and the software that maintains it. The theory is not difficult.
What Is a Database?
In a book about databases. how best to glaze them for color. What is a database? Our answer is simple: A database is an orderly body of data. a DNA sequence. This answer. Most importantly. a histogram. we mean the everyday world that we experience through our senses and speak of in common language. is introduced. The type can range from the simple to the very complex. We offer this definition: A datum (or data item) is a symbol that describes an aspect of an entity or event in the real world. For example. in particular. you must first learn the properties of the tiles from which you will assemble your picturestheir weight. To begin. a code. and a software object can each be regarded as a 19
. a number. If you wish to become a mosaicist. its ISBN number. if you want to work with databases. however. data is difficult to define exactly. This chapter is theoretical rather than practical. and how a database manages data. the score. a data item has a type. the book in your handan entity in the real worldcan be described by data: its title. Or consider how a baseball gamean event in the real worldis described by data: the date on which the game was played. although other types of databases are also discussed. you should take the time to read through this chapter and become familiar with the theory it describes. the name of its publisher. Types of data Although data are derived from entities and events in the real world. your name. the names of the winning and losing pitchers. the names of the teams.Chapter 2: The Relational Model
This chapter discusses what a database is. you will find it easier to think coherently about databasesand therefore find it easier to solve your data−related problems. We use data to portray practically every entity and event in our world. the proper materials for gluing them into place. data have properties of their own. However. The relational model for databases. Each data element is a tile in the mosaic used to portray an entity or event. the year of its publication and the city from which it was published are all data that describe this book.
What are data?
Despite the fact that we use data every hour of every day. An image. but you have work to do and problems to solve. the names of its authors. you should learn the properties of data so you can assemble them into data−portraits of entities and events in the real world. In the same way. raises two further questions: • What are data? • What does it mean to maintain a body of data? Each question is answered in turn. and so on. if you grasp the theory. Some of it may seem arcane to youafter all. and much of it simply codifies common sense. theory is fine. it is reasonable to ask. By real world. where it was played.

but the interval between them is not defined precisely. the calendar year is not a number of absolute scale. However. these four data types give increasingly complex ways to describe entities or events. There are four statistical data types: A nominal datum names an entity or event. a mans name is a nominal datum. Ordinal An ordinal datum identifies an entity or events order within a hierarchy whose intervals are not exactly defined. We cannot cover the range of complex data types herethese types usually are tailored for a particular task. temperature measured as degrees Kelvin (that is. there is one complex data type that you will use continually: dates. You can say exactly what the interval is from one point on the scale to another. For example.type of data. a soldiers military rank is an ordinal datum: a captain is higher than a lieutenant and lower than a major. degrees above absolute zero) is a ratio datumfor 12 degrees Kelvin is both 8 degrees hotter than 4 degrees Kelvin. An address is nominal. Interval An interval datum identifies a point on a scale whose intervals are defined exactly. As you can see. but you cannot compute a ratio between two measurements. but it is not twice as far removed from the beginning of time. Ratio A ratio datum identifies a point on a scale whose intervals are defined exactly. Because many of the questions that you will want to ask of your database will be statisticalfor example. the statistical types are among the most common that you will use in a database. 20
. among the most vexing. The type date combines information about the year. and whose scale has a clearly defined zero point. Another example is a teachers evaluation of a students effort: good is above poor and below excellent. and what properties each possesses. and ratio more than interval. month. minute. If you can grasp what these data types are. but again the intervals between them are not defined precisely. or what was Wade Boggs batting average in 1985these data types will be most useful to you. For example. and second. you will be better prepared to work with the data in a database. and because of their complexity.
Statistical data types
Amongst the most commonly used types of data are the statistical types. For example. and information about daylight savings time. Ordinal data can hold more information than nominal. information about hour. interval more than ordinal. and so is a telephone number. time zone.000 years of time later than the year 1000. For example.
Complex data types
Nominal
Beyond the simple statistical data types that are the bread and butter of databases lies an entire range of complex data types. The year 2000 is exactly 1. As we mentioned at the beginning of this section. day. so is his sex. and three times as hot in absolute terms. but whose scale does not have a clearly defined zero point. Dates are among the most common data items that you work with. but simply a count of years from some selected historical eventfrom the foundation of the state or the birth of a noteworthy person. what was the average amount of money that your company received each month last year. These data are used to perform the classic statistical tests.

a DNA sequence can be regarded as a type of complex data. The following subsections discuss this in a little more depth. to discover how many years lie between 1895 and 1987. Because they rest upon an absolute scale. and inferiority. each complex data type supports a handful of specialized operations. These data are compared for equality. Data usually are compared for equality. For example. superiority. they are ideal for an entire range of mathematical operations. they often are compared lexicallythat is. why would we record how many runs a baseball team scored in a game. The following briefly summarizes the operations that usually can be performed upon each type of data: Nominal Data are compared only for equality. The following comparison operations can be performed on DNA sequences: • Compare length of sequences • Compare length for equality • Compare homology at percent x
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. a persons name is a nominal datum. Interval data often are subtracted from one another to discover the difference between them. or whether one is superior or inferior to the other. for example. and usually you will compare two names to determine whether they are the same. subtraction. After all. you can subtract one from the other to discover the interval between them. one will compare two soldiers ranks to determine whether one is superior to the other.Operations upon data It is worth remembering that we record data in order to perform operations upon them. superiority. They usually are not compared for inferiority or superiority. It is not common to perform mathematical operations upon ordinal data. Mathematical operations perform a mathematical transformation upon data. If the data are text (as is usually the case). or inferiority. multiplication. The transformation can be arithmeticaddition. For example. or divisionor a more complicated transformation (for example.
Statistical data types
The data operations that are usually performed upon the statistical data types fall into two categories: comparison operations and mathematical operations. Data usually are compared for equality. except to compare that data item with the number of runs that the other team scored? A data items type dictates what operations you can perform upon that data item. computing a statistic). For example.
Ordinal
Interval
Ratio
Complex data
Usually. compared to determine which comes earlier in alphabetical order. and inferiority. superiority. nor are mathematical operations performed upon them. Comparison operations compare two data to determine whether they are identical.

a data item that has type ratio can have the domain temperature. The domain states what the data item describes. and the data item with domain temperature will not have a value of Catherine.
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. a domain is well defined. the transformation operations are strictly tied to the special nature of the data. We have offered a definition of data. by definition. even though both have type ratio. Here. can be performed upon DNA sequences: • Determine coding frame • Determine coded amino−acid sequence • Compute percent purine • Compare percent pyrimidine • Determine location of hairpins or palindromes • Determine complementary sequences As you can see. even though both are ordinal. For example. a body temperature (an interval domain). A data item can be compared only with another data item in the same domain.The following transformations. a soldier has a name (a nominal domain). For example. comparing the name of an automobile with the name of a human being will not yield a meaningful result. Before leaving domains for the moment. they are said to be related to each other. database was defined as an orderly body of data and the software that maintains it. we must discuss another fundamental issue: what it means to maintain a body of data. although the comparison operations are not. a data item has a domain. To summarize: We gather data to interpret them.6.
What does it mean to maintain a body of data?
At the beginning of this chapter. A data items type sets the operations that you can perform upon that data item. • The domain also determines the values the data item can hold. For example. an entity or event in the real world has many aspects. a rank (an ordinal domain). nor will comparing a military rank with the grades on a report card yield a meaningful result. here are two additional thoughts: • First. however. and therefore is described by a combination of many domains. Or a data item that has type nominal can have the domain name. Likewise. it is not meaningful to subtract the number of runs scored in a baseball game from the number of points scored in a basketball game. For example. and operations help us to interpret data. analogous to mathematical operations. although both are nominal data. the data item with domain name will not have a value of 32. and an age (a ratio domain). Domains In addition to type. We will return to the subject of domains and their relations shortly. well defined means that we can test precisely whether a given data element belongs to the domain. and therefore defines what values that the data item can hold: • The domain determines what the data item describes. now we will describe what it means to maintain a body of data. When a group of domains each describe a different aspect of the same entity or event. • Second. But first.

The database software should let us retrieve data by naming the bins and slots that hold themthat is. each size in its own slotthen each item becomes much more useful. maintaining means that we must perform these tasks: • Organize the data • Insert data • Retrieve data • Delete data • Update data • Maintain the datas integrity Each task is discussed in turn. add new bins and slots. Organize data The first task that must be performed when maintaining a body of data is to organize the data. and nuts that are jumbled together. • Give each bin and each slot a label. because we can quickly find the exact item that we need for a given task. • When necessary. the software should help us to put each datum into its appropriate bin and slot. Delete data Sometimes we need to delete data from our database. • Build slots within each bin to hold the data. However. we might as well not have bothered to store them in the first place. so that we do not have to search the entire database to see what the database holds. if the screws.In brief. Our next task then is to retrieve the data. Inserting data After our software has helped us to build a warehouse for our dataregardless of whether or not we have any datathe next step is to insert data into the database. and update the catalogue to describe them. To organize data involves these tasks: • Establish a bin for each category of data to be gathered. nothing more. It should remove only the data we addressnothing less.
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. If it sounds as if were describing a warehouse instead of a software system. data are worthless. one slot for each datum. Put simply. both a warehouse and database are designed to organize things. it should let us address the data. And so it is with data: without firm organization. Retrieve data If we cannot read our data after we have stored them. The database software should let us do so by address. washers. • Write a catalogue of the bins and their slots. Theres nothing more useless than a pile of screws. which is not a coincidence: after all. washers. It should also give us an orderly way to examine the data that we have retrieved. to tell us what it holds. and nuts are well organizedeach type in its own bin.

an author. Maintaining integrity Maintaining a database involves these five tasksorganization. maintaining the integrity of your data is extremely important. and an ISBN number. of course. The rest of this chapter examines the theory behind maintaining these groups of related data. or how data can be joined together to form a portrait of an entity or event in the real world. for example. a city of publication. There is a difference. however. a database that records information about books. inserting.
Relationality
So far. but each has meaning only when it is coupled with the other data that describe a book. We discuss throughout the rest of this chapter just what you must do to maintain data integrity. which logic is dictated by the nature of the entity or event that we are studying. and insert the modified data into the database. we have spoken of the data within a database as if each datum were something unto itself and bore no relation to the other data within the databaseas if a database were comprised of randomly collected observations that had nothing to do with each other. Each data item has its own type and its own domain. or relations. A number of designs for database management systems have been proposed over the years. but it does so in such a way as to maintain the integrity of the data. between simply performing these tasks.
The Relational Model
A database management system (DBMS) is a tool that is devised to maintain data: to perform the tasks of reading data from the database. while preserving the integrity of the data. updating the data within the database. One more concept must be introduced: relationality. In other words. the data that we collect are related to each other. and updating. After all. then delete the old data. It is best that our software handle this tricky task for us. Doing this by hand. deleting. Strictly speaking. and several have found favor. and inserting data into the database. Consider. As you can imagine. we could simply retrieve the data from our database. modify them. can cause problemswe can easily make a mistake and wreck our data rather than modify them. To this point. There is a logic to the data that we collect. is not the case: we go to the trouble of building a database because we wish to maintain a body of data for a well−defined purpose. the update task is not a necessary part of our database−maintenance system. a year of publication. we have presented our definitions: what data are and what it means to maintain data. This book concentrates on one designthe relational databasefor three reasons:
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. a publisher. this means that you must protect the data from errors that dilute the meaning of the data. retrieving. In brief. The relations among data are themselves an important part of the database. Much of the work of the database software will be to maintain integrity not just among data and within data.Update data The last task is to update data within the database. but among these related groups of data. A database−maintenance system not only performs these tasks. Each book has a title. and performing them well. This. however.

in a paper published on August 19. you can use it to solve a great variety of problems. The subsequent history of the relational database was one of gradual development leading to widespread acceptance. and Thompson and Ritchie would soon boot the UNIX operating system for the first time. IBMs effort in the early 1970s. You may well ask why we study the model when we can lay our hands on an implementation and work with it. The term relation has a precise definition. in particular Oracle. Beneath all this activity. Codd. Informix. you will have acquired a tool that will help you work with every design for a database. led to the development of Ingres and the QUEL inquiry language. however. as its name implies. Armstrong and Aldrin had walked on the moon just weeks earlier. the relational model is well worth learning. a mathematician with IBM. • The relational database is the only database that is built upon a model that has been proved mathematically to be complete and consistent. In the late 1970s. two groups. lies Codds original work. Today.
Structure of the relational model
The relational model. Codds insights into the design of databases will continue to be built upon and extended. however. we ask that you remember that the relational model is precisely thata model. • The relational database is robust. however. that if you can grasp the relational model. that is.
What is the relational model?
The relational model was first proposed by Edgar F. In the early 1970s. We do say. the model gives us a yardstick against which we can measure implementations. When you begin to grapple with difficult problems in data modeling and data management. we can judge how well a given package implements the model. took up Codds ideas. The Berkeley group. commercial products began to appear. is built around relations. The relational model is a model The rest of this chapter presents the relational model. but it is unlikely that they will be superseded for years to come. you will be glad to have such a tool available.
25
. This is not to say that the relational database is the only one that should be used. There are two reasons: • First. a construct that exists only in thought. led to IBMs System/R and Structured Query Language (SQL).• The relational database is by far the most important commercially. led by Michael Stonebraker. and Sybase. Berkeley. the relational model gives us a tool for thinking about databases. As you can see. or that the competing designs should be discarded. to help you grasp the definition. the major relational−database manufacturers sell billions of dollars worth of products and services every year. Before we go further. 1969. If we know the rules of the relational model. one at IBM and the other at the University of California. To put that date into its historical context. It is difficult to overestimate the importance of this fact. • Second. we will first review what we said earlier about data.

interval. the body of a relation that describes a baseball game would hold data that described individual games. these four data use only two domains: the name of the home team and the name of the visiting team each use the domain of names of major league baseball teams. and together. the heading for a relation that described a baseball game would name three domains: teams. The heading of a relation Again.• A datum describes an aspect of an entity or event in the real world. The games score is worth knowing. For example. as you can see. Our purpose in collecting data is to describe an entity or event in the real world. In practice. and score. When we record information for a baseball game. As you can imagine. If we know the teams without knowing the score. For example. it is important that we ensure that these domains are used unambiguously. our knowledge is incomplete. Except in rare instances. and the runs scored by the home team and the runs scored by the visiting team both use the domain of baseball game runs. called the body. • The second part. and then the body. a relation has two parts: • The first part. a datums value is the member of the domain set that applies to the entity or event being described. A datum has three aspects: its type. we do not really know anything about the game. or it can be a complex type (for example. or ratio). • The number of runs scored by the visiting team. the team. • A datum has a type. likewise. these domains form a relation that describes a baseball game. date. ordinal. called the heading. • A datums domain is the set of values that that datum can contain. but only if we know the names of the teams playing the game and the date upon which the game was played. For example. A data element is one tile in a mosaic with which we portray the entity or event. if we know the score and the date. names the domains that comprise the relation. The next two subsections discuss the heading of a relation. Then we rejoin the head to the body. rather. so that you can see the relation as a whole. but do not know the teams. So now we are zeroing in on our definition: A relation is a set of domains that together describe a given entity or event in the real world. but it must be well defined. lets consider the example of the score for a baseball game. an entity or event must be described with multiple data elements that are related to each other by the nature of the entity or event we are describing. its domain. a data element cannot describe an entity or event by itself. A domain can be anywhere from small and finite to infinite. and score each is a domain. The type may be one of the statistical types (nominal. We humans 26
. • Finally. • The name of the visiting team. However. then the value for the datum that describes the team that plays its home games in Chicagos Wrigley Field is Cubs. date. For example. we want to record the following information: • The name of the home team. For example. consider a baseball game. a date). • The number of runs scored by the home team. These are four data. if the domain is the set of all major league baseball teams. gives the data that describe instances of the entity or event that the relation describes. and its value.

complete. A computer database. which we described in the previous example. lets translate our baseball game into the heading of a relation. These two attributes let us identify major league baseball teams. which has the type of date. such as the teams league or its division. these six attributes let us identify the outcome of any major league baseball game ever played. when we read Atlanta Braves. We need this in case the teams played a double−headerthat is. because we bring information to our reading of a score that helps us to disambiguate the data it presents. we introduce one last element to our definition of a domain: the attribute. The attribute−name must be unique within the relation. When we do so. To help remove ambiguity from our relation. We could add more attributes to this relation. Weve enclosed each domains name in angle brackets (that is. For the sake of simplicity. Likewise. for example. which consists of the names of all stadiums in North America. Therefore. the domain name to the right. we know that the information on the same row of print as that of the team name applies to that team.
Attributes: baseball game example
To see how this works. however.do not always grasp how important it is to abolish ambiguity. An attribute identifies a data element in a relation. This attribute has domain MLBT. but for now. and free of ambiguity. Likewise. 27
. • Home stadium (HS). and "major league baseball team" becomes MLBT. it is vital that what you tell it is clear. this domain can only have values 1 or 2. These data tell us the outcome of the game. It has two parts: the name of its domain and an attribute−name. we know that that string names a baseball teamin other words. Our relations heading now appears as follows:
<HT:MLBT> <VT:MLBT> <HT−RUNS:BR> <VT−RUNS:BR> <DG:GDAT> <GNUM:NUM> Attributes: baseball team example
For another example. We add two other data so that we can identify each game unambiguously: • Date the game was played (DG). our relation becomes as follows:
<HT:MLBT> <VT:MLBT> <HT−RUNS:BR> <VT−RUNS:BR>
The name of the attribute appears to the left of the colon. The attribute has a domain of "game date" (GDAT). The domain limits the value of this attribute to dates that have had major league baseball games played on them. For example. nor is it played during the winter. played two games on the same day. major league baseball was not played before 1876. < and >) to make it a little more readable. that that datum belongs to the domain of names of major league baseball teams. we will abbreviate the names of our domains: baseball runs becomes BR. we will abbreviate the names of the attributes: "home team" becomes HT and "visiting team" becomes VT. consider a relation that describes major league teams in detail. This attribute has domain stadium (STAD). what we have here is sufficient. Such a relation will have at least two attributes: • Name of the team (TEAM). • Number of the game on that date (GNUM). has no such body of knowledge upon which to draw: it knows only what you tell it. Together. This attribute has domain NUM.

first or second game on that date). Each row consists of one data item from each of the relations attributes. we will use the more familiar word row instead of tuple. Or consider the relation that describes major league baseball teams. and number of the game (that is. however. for example. the header identifies the six attributes that comprise the relation: home team.
28
. this word is more precise than row is. Consider. to help make the following discussion a little more accessible. visiting team. The following shows some rows for it: Header:
<TEAM:MLBT> <HS:STAD>
Body:
Braves White Sox Angels Mariners Cubs Turner Field Comiskey Park Anaheim Stadium Safeco Field Wrigley Field
These rows identify the team that played in the games described in baseball game relation. The body of a relation consists of rows of data. the baseball game relation we described earlier. and a double−header in which the Angels beat the Mariners in the first game but lose to them in the second game. Each of the four rows gives the score of a gameone in which the Braves at home are beaten by the Cubs. The following shows the relations heading and some possible rows: Header:
<HT:MLBT> <VT:MLBT> <HT−RUNS:BR> <VT−RUNS:BR> <DG:GDAT> <GNUM:NUM>
Body:
Braves White Sox Angels Angels Cubs Brewers Mariners Mariners 3 2 2 6 5 8 1 7 05/05/95 05/05/95 05/05/95 05/05/95 1 1 1 2
In this example. The literature on relational databases uses the word tuple for a set of values within a relation. date the game was played. runs scored by the visiting team. the White Sox at home are beaten by the Brewers. runs scored by the home team.The relations heading appears as follows:
<TEAM:MLBT> <HS:STAD>
The body of a relation Now that we have defined the heading of a relation. which is the relations abstract portion. For a number of reasons. the next step is to define its bodythe relations concrete portion.

However. we have seen that a relation has two parts: the heading. When we speak of an attribute. However. item of information. Each row within a relation is unique.HT. for our exercise.
No ordering
Neither the attributes in a relation nor its rows come in any particular order. So. it cannot be another relation. it must have three specific properties. or decompose. but it is an important part of database design. and the body. and. This means that a datum within a relation cannot be a structure or a formula (such as can be written into a cell of a spreadsheet). Semantic normalization is not a part of the relational model. most importantly. which consists of rows that give instances of the attributes that are named in the heading. we can refer to attribute HT in relation GAMES as GAMES. This is an important aspect of the relational model. we cannot address a row by its position 29
. Relational theory does not demand that a relation have a name. we display a relation in the form of a table. For a collection of attributes to be a true relation. this is just a convention.Naming relations For the sake of convenience. and only one. and we will name our second relation (the one that identifies team) BBTEAMS. If you wish to define a domain whose members are themselves relations. regardless of the order in which those attributes appear. yet make it perfectly clear just which instance of domain we are referring to. you must first break down. Cross Reference We discuss semantic normalization further in Chapter 4. The process of normalization is an important aspect of designing a database. We use the term semantic normalization to describe the process by which a database designer ensures that each datum in each of his relations contains one. however. With this notation.
No duplicate rows
This is an important point that is often overlooked: a relation cannot contain duplicate rows. we will name our first relation (the one that gives the scores of games) GAMES. For example. we will prefix the attribute with the name of the relation that contains it. we will give names to our relations. This process of breaking down a complex attribute into a simpler one is part of the process called normalization. Atomic means that an attribute cannot be broken down further. This is an important property. it is useful to be able to refer to a relation by a name. Properties of a relation So far. By convention. Because rows come in no particular order. we can use the same domain in more than one relation. when we discuss database design. and then insert those data into the relation. because it lets us identify (or address) each row individually.
Atomic values
Every attribute within a relation is atomic. each relation into the atomic data that comprises it. We discuss it in some detail in Chapter 4. which identifies the attributes that comprise the relation. so we will give a name to each of our relations. using a period to separate the names of the relation and the attribute. The absence of ordering means that two relations that are comprised of the same set of attributes are identical.

but SQL allows its tables to hold duplicate rows. However. the rule of no duplicate rows ensures that we can address each row individually. date of game. The following subsections introduce each. and GNUM (that is. and game number) identify a game uniquely. Most often. The property of uniqueness guarantees that we can address a row by using all of the attributes of the row within the query that we ask of the relation. and that row alone. It is also an important point upon which the relational model and SQL diverge: the relational model forbids a relation to hold duplicate rows. attribute TEAM is the primary key for relation BBTEAMS. if we added attribute HT−RUNS to the primary key for attribute GAMES. for example. because we may know some aspects of the entity or event that the rows describes. the date. what use is a filing cabinet if we cannot retrieve the papers that we put into it? As we noted above. we know the teams. or one row for the Orioles. Therefore. this may not be very useful to us. we usually query a database to find some item of information that we do not know. attribute TEAM uniquely identifies each row within the relation: the relation can have only one row for the Red Sox.
Primary keys
A primary key is a set of attributes whose values uniquely identify a row within its relation. After all. the date. The only way we can address a row is by finding some value within the row that identifies it uniquely within its relation. Keys come in two flavors: primary keys and foreign keys. After all. Thus. When were examining the data about a baseball game. The only restriction that the relational model places upon a primary key is that it cannot itself contain a primary keythat is. the uniqueness property of a relation is especially important to the task of retrieval: that each row within the body of a relation is unique guarantees that we can retrieve that row. but the number of runs scored by the home team is extraneous to the task of identifying each row uniquely. For example. DG. our relation for baseball scores. and the number of the gamebut we do not know the number of runs that each team scored. If we already know all six attributes of the row (that is.
30
. A primary key can also combine the values of several attributes. home team. and in particular for the writing of a database application. the primary key would still identify the row uniquely. and the number of runs that each team scored). we know the teams involved in the game. Consider. to recover from the database the information that we have put into it. Keys Arguably. but not others. For example.within the relation. it would be most useful if we could use the information that we do know to find the information that we do not know. And there is such a methodwhat the relational model calls keys. then theres no reason for us to query the database for that row. a primary key cannot contain attributes that are extraneous to its task of identifying a row uniquely. however. the attributes HT. the game number. For example. in relation GAMES. This property has important implications for database design. in relation BBTEAMS. the most important task that we can perform with a database is that of retrieval: that is.

if a row in GAMES sets the value of attribute GAMES. The product of each operation can itself be used as the input to yet another operation. (And there will not be a quiz at the end of this section!)
Relational algebra Relational algebra performs operations upon relations. For example.TEAM.Foreign keys
A foreign key is a set of attributes whose value equals that of a primary key in another relation. we can build elaborate expressions. One of the most important parts of the relational model is the language with which we examine and compare relations. Thus. For example. when we discuss the issue of database integrity. attribute GAMES.HT to the value of "Orioles. The first four are standard operations for manipulating sets. The eight operations come in two groups of four.HT is joined to attribute BBTEAMS. Please make note of this term. thus. Attributes HT and VT in relation GAMES also name baseball teams.
Relational algebra and relational calculus
The subject of foreign keys introduces the idea of how relations are hooked together. In other words. Foreign keys have several important properties: • The attributes that comprise a foreign key must have the same domains as the attributes to which they are joined. Note Please note that the terms relational algebra and relational calculus have little to do with the algebra and calculus that you attempted to learn in high school. In fact. The linking of two relations through a foreign key is called a join.TEAM to "Orioles." or an error has occurred. not just some of them. from these eight elementary operations. F." then relation BBTEAMS must have a row that sets the value of attribute BBTEAMS. a foreign key cannot point to nowhere. Each operation builds a new relation that holds its output. a relation does not have to have a foreign key. Codd. who invented the relational database. The relational model offers two such languages: relational algebra and relational calculus. a foreign key refers to one row in the other relation. and build new relations. therefore. The core of the relational algebra is eight basic operations. and is the primary key for that relation. These were first described by E. You do not need to know either algebra or calculus to grasp the principles of relational algebra and relational calculus. • The relation to which the foreign key is joined must contain a row that contains the data that comprise the foreign key. 31
. the attribute TEAM in relation BBTEAMS names a baseball team. or joined. A relation must have at least one primary key. each can serve as a foreign key to relation BBTEAMS. however. • A foreign key must match all of the attributes in the primary key to which it is joined. we can use foreign keys to build new relations. by joining together all or part of the relations that a foreign key joins. Thus. These are conventional terms that describe how we work with relations. This issue is discussed in more detail later. because you will see it frequently throughout the rest of this book.

MYGAMES is our familiar baseball−game relation:
<HT:MLBT> Braves White Sox Angels Angels <VT:MLBT> Cubs Brewers Mariners Mariners <HT−RUNS:BR> 3 2 2 6 <VT−RUNS:BR> 5 8 1 7 <DG:GDAT> 05/05/95 05/05/95 05/05/95 05/05/95 <GNUM:NUM> 1 1 1 2
YOURGAMES has the same structure as MYGAMES. By identical structures. We first discuss the four standard operations. and then the four special ones. consider two relations. The union of these two relations produces the following:
<HT:MLBT> Braves White Sox Angels Angels Reds Red Sox <VT:MLBT> Cubs Brewers Mariners Mariners Marlins Yankees <HT−RUNS:BR> 3 2 2 6 7 3 <VT−RUNS:BR> 5 8 1 7 6 4 <DG:GDAT> 05/05/95 05/05/95 05/05/95 05/05/95 05/05/95 05/05/95 <GNUM:NUM> 1 1 1 2 1 1
As you can see. if a row appears in both parent relations.the other four operations are designed to manipulate relations. Therefore. consider the relations MYGAMES and YOURGAMES described above.
Intersection
The intersection operation compares two relations. For example. the product of the union operation holds all rows that appears in either parent relation. The relation that the union operation builds. For example. As with the union operation. it builds this relation: 32
. and builds a new relation that contains every row that appears in either relation. the two relations that the intersection operation compares must have identical structures. MYGAMES and YOURGAMES. When we perform the intersection operation upon those two relations. and builds a relation that contains an instance of every row that appears in both of the relations it compares. does not contain duplicate rows. it appears only once in the product relation. For a union operation to yield a meaningful result.
Union
The union operation compares two relations. we mean that the relations be comprised of the same set of attributes (although the attributes may have different names). the relations that are being compared must have identical structures. of course. but its body is different:
<HT:MLBT> Reds White Sox Red Sox <VT:MLBT> Marlins Brewers Yankees <HT−RUNS:BR> 7 2 3 <VT−RUNS:BR> 6 8 4 <DG:GDAT> 05/05/95 05/05/95 05/05/95 <GNUM:NUM> 1 1 1
The two relations have one row in commonthe one that describes the game in which the Brewers played the White Sox in Chicago.

the intersection operation produces a new relation that contains the one row common to both relations that we compared. it matters which relation comes first. For example. As with the union and intersection operations. Thus. Because this operation determines which rows in the first relation are not in the second. if we perform a difference operation upon relations MYGAMES and YOURGAMES. the difference operation produces a relation whose body contains every row that is in MYGAMES and is not in YOURGAMES. Thus. consider two relationsnamed. (The Cartesian product is named after the French mathematician René Descartes. It compares two relations and builds a new relation that contains every row that is in the first relation and not in the second. determines how two relations differ. intersection.) Unlike the union. as its name implies. we receive the following relation as its product:
<HT:MLBT> Braves Angels Angels <VT:MLBT> Cubs Mariners Mariners <HT−RUNS:BR> 3 2 6 <VT−RUNS:BR> 5 1 7 <DG:GDAT> 05/05/95 05/05/95 05/05/95 <GNUM:NUM> 1 1 2
As you can see. FIRST and SECONDthat are each comprised of a single attribute. who first described this operation. and restriction operations.<HT:MLBT> White Sox
<VT:MLBT> Brewers
<HT−RUNS:BR> <VT−RUNS:BR> <DG:GDAT> <GNUM:NUM> 2 8 05/05/95 1
As you can see. Relation FIRST contains the follow attribute and rows:
<NUMBER:INT> 1 2 3
SECOND contains the following attribute and rows:
33
. the Cartesian−product operation does not require that the relations being compared be identically structured. the operation
difference MYGAMES YOURGAMES
will not give the same result as operation:
difference YOURGAMES MYGAMES Cartesian product
The Cartesian−product operation builds a new relation by joining every row in one relation with every row in a second relation. To give a simple example of this operation. respectively.
Difference
The difference operation. the row that gives the score for the White Sox−Brewers game is eliminated. the two relations that the difference operation compares must have identical structures. because it appears in both parent relations.

the question arises." Doing so produces the following relation:
<HT:MLBT> Angels Angels <VT:MLBT> Mariners Mariners <HT−RUNS:BR> <VT−RUNS:BR> <DG:GDAT> <GNUM:NUM> 2 1 05/05/95 1 6 7 05/05/95 2
The new relation that it builds has the same structure as its parent relation. this operation in effect pasted each row from SECOND onto the end of each row in FIRST. it is useful with the restrict and project operations. We could use the project operation on relation MYGAME to eliminate all attributes except HT and HT−RUNS. difference. The restrict operation examines a single relation. It builds a new relation whose body consists of rows selected from the original row using specified criteria. Naturally. it does for attributes what the restrict operation performs for rows.
Restrict
The first four operationsunion. The next four operations are tailored for use with relations.<LETTER:ALPHA> A B C
The Cartesian−product operation creates the following relation:
<NUMBER:INT> 1 2 3 1 2 3 1 2 3 <LETTER:ALPHA> A A A B B B C C C
As you can see. We will see this demonstrated in a moment. we can perform the restrict operation upon the relation MYGAMES to select the rows in which HT equals "Angels. For example. intersection. A programmer must give to this operation the criteria with which it selects rows from a relation. It builds a new relation whose body consists of attributes selected from the original relation.
Project
The project operation examines a single relation. thus producing the following relation:
<HT:MLBT> Braves <HT−RUNS:BR> 3
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. but its body is restricted to the rows that meet the requested criteria. and Cartesian productare used to manipulate sets of all types. not just relations. In particular. to create every possible unique row from bodies of the two relations. In effect. suppose that we were just interested in the number of runs scored by the home team. What good is this? The answer is that although the Cartesian product of two relations is not much use by itself can be very useful when combined with other operations. For example.

One last point should be made: the joining we described here is only one of many ways in which two relations can be joined.
Divide
The divide operation is a specialized operation that combines the restrict and project operations to divide one relation by another. This type of join is called the natural join. it is a combination of the Cartesian product. if we use the join operation to fuse relation GAMES with relation STADIUMS based on a shared value in attribute HT. Consider one relation. and project operations. The join operation lets us refine the Cartesian product by selectively joining the rows based on the contents of one or more attributes that are shared by the two parent relationsthat is. based on a foreign key. this example in effect adds the attribute of home stadium to each row in MYGAMES. an atomic operation: in fact. The join also eliminated one instance of the shared attribute. dont worrythe divide operation is more easily explained by example than by definition. A foreign key must join the relation to be divided and the relation that does the dividing. For example. because it is redundant. The divide operation finds every value in the dividend relations nonkey attributes in which those nonkey attributes share a row with every value in the divisor relations foreign key. except that it uses common values from one or more attributes in the two relations to build the new relation selectively. It resembles the Cartesian−product operation. If this seems obscure. Because it is so useful. The natural join is the most commonly used of the join operations. however. we will treat it as if it were an atomic operation. restrict. however. We use it again and again throughout this book. we get the following:
<HT> Braves White Sox Angels Angels <VT> Cubs Brewers Mariners Mariners <HT−RUNS> 3 2 2 6 <VT−RUNS> 5 8 1 7 <DG> 05/05/95 05/05/95 05/05/95 05/05/95 <GNUM> 1 1 1 2 <HTS> Fulton County Stadium Comiskey Park Anaheim Stadium Anaheim Stadium
As you can see. The join operation is one of the most useful of all operations in the relational algebra. and usually the one meant when one speaks of joining two relations. It is not.White Sox 2 Angels 2 Angels 6 Join
The join operation builds a new relation by fusing two existing relations. named FRUITS:
<FN:NAME> <DESC:ADJ> apple red apple crisp apple tart cherry red cherry sweet cherry stone orange orange orange juicy orange sweet
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.

His suite of operations. and builds a relation as its output. In our example. the divide operation is a hybrid operationthat is. These operations are sometimes called theta operations. In this example.peach peach peach
fuzzy juicy sweet
Now. does not include comparison operationsthat is. To meet this need. it actually combines the restrict and project operations to perform a special task. however.
Comparison operations
Each of Codds eight basic operations manipulates one or two relations. we find every value in the nonkeyed attribute of FRUITS that shares a row with every value in the foreign key of SOMEATTS. consider the relation SOMEATTS:
<DESC:ADJ> red sweet
A foreign key on the attribute DESC joins FRUITS and SOMEATTS. Anyone who has programmed knows how important these are to any programming language. The theta operations have the following syntax:
expression theta expression
where theta is one of the following: • = Equals • != Not equals • <= Subset • < Proper subset • >= Superset • > Proper superset
36
. Codd proposed a further set of comparison operations. operations that compare two relations for similarity or dissimilarity and return a simple value that indicates whether they meet the test. because in Codds notation each operation in this set was represented by the Greek letter theta. the divide operation will find every value of attribute FRUITS:FN that shares a row with each of the values given in attribute SOMEATTS:DESCthat is. When we divide FRUITS by SOMEATTS. it will find every fruit that is both red and sweet. As we noted above. As you will see later. the divide operation produces the following relation as its output:
<FN:NAME> cherry
This is because only cherry is both red and sweet. this operation can be quite helpful in manipulating relations.

which we described in the previous section.DG = 05/05/95 AND MYGAMES.HT WHERE MYGAMES. For example. we use != for not equals rather than an equal sign with a slash through it. For example. In particular. In fact. These attributes will be populated with data that are copied from existing relations. It consists of one or more attributes. we discuss only the row−oriented relational calculus. the above notation is a little misleading. As some commentators have noted. This expression uses a comparison operator (=. the selection−expression is introduced by the keyword WHERE. Rather. Relational calculus does not bother with the details of how to build the relation. consider the relation MYGAMES.HT−RUNS > MYGAMES. unlike the relational algebra. However. or >=) to couple an attribute with either another attribute or with a constant. and the home team won:
MYGAMES. but you can rename one or more of them if you wish. You probably have noticed that we speak of relational calculus instead of the relational calculus. whereas relational calculus is descriptive. there are two commonly used systems of relational calculus: row−oriented calculus and domain−oriented calculus. you can also say in the other. >. the theta operations on the whole are well selected and useful. The two systems are logically equivalent: whatever you can say in one. In other words. <=. By convention. The following creates a new relation that consists of the attribute HT. !=. Each form of calculus is a model for commonly used relational query languages.
Relational calculus Relational calculus. when we discuss SQL. it lets you formulate the relation that you wish to build.VT−RUNS
As you can see. For the sake of brevity. Expressions can be coupled with the logical operators AND and OR. the row−oriented relational calculus is the basis for IBMs Structured Query Language (SQL). Cross Reference Examples of their use are given in Chapter 3. the operations >= and < do not necessarily yield inversions of each other. <. does not describe operations upon relations. The domain−oriented calculus is the basis for the Query−by−Example (QBE) language. the names of the attributes are separated by commas. 37
. Each attribute must already reside in an existing relation. relational algebra is prescriptive. the selection−expression sets the conditions under which a row can populate the newly defined relation. selection−expression describes how to select rows from existing relations. By convention. and populates that attribute with the name of the winning team in games where the game was played on May 5.Please note that the above notation uses C−language operators rather than the mathematical symbols that Codd originally used for the same operations.
Syntax
The row−oriented calculus has this syntax:
target−relation selection−expression
target−relation defines the relation that is to be built. 1995.

such as for or while in the C language. whereas the calculus is descriptive: the algebra says what to do. You wont be too far off the mark if you think of relational algebra as being a kind of relational third−generation language.VT−RUNS AND (EXISTS STADIUMS (MYGAMES.HT−RUNS > MYGAMES. in which you describe the operations. 1995:
HTS:STAD WHERE FORALL MYGAMES (MYGAMES. in order to obtain the result that you have in mind.HT−RUNS > MYGAMES. EXISTS states that a row exists that fulfills a given condition.DG = 05/05/95 AND MYGAMES. As a rule of thumb. EXISTS declares that selection−expression should be executed if at least one row fulfills the condition set in the EXISTS clause.HTS = Wrigley Field))
Finally. 1995but only if that team played in Wrigley Field:
MYGAMES. this keyword lets you select rows based on one or more values in a row that is not itself a candidate for selection.HT = STADIUMS. whereas the calculus describes the result that is to be obtained.EXISTS and FORALL
The keyword EXISTS can be used to refine a selection. whereas FOREACH is more like a loop operator. on the other hand.DG = 05/05/95 AND MYGAMES. Relational algebra versus relational calculus Codds reduction algorithm proves that the calculus and the algebra are equivalent: every statement within a relational calculus can be reduced to a set of expressions in the relational algebra. The following builds a row that holds the name of the stadium in which the home team won a game on May 5. The following code also selects the names of each team that won at home on May 5. step by step. the keyword FORALL executes selection−expression for each row that meets the given condition. in which you describe the outcome that you want but let the system determine the algebraic steps 38
. So.VT−RUNS)
The two conditional keywords differ subtly but significantly. In effect.HT AND MYGAMES. FOREACH. For example. For example. and each set of operations within the relational algebra can be summed up by a statement in a relational calculus. which executes an expression for every value that meets its condition. which turns on or off the execution of an entire expression. how does the relational algebra compare with relational calculus? As we noted earlier. described above. declares that selection−expression must be executed for every row that fulfills the condition set in the FOREACH clause. This difference is important.HT AND STADIUMS.HT WHERE MYGAMES. consider the relations MYGAMES and STADIUMS.HT = STADIUMS. consider again the relations MYGAMES and STADIUMS. and think of the relational calculus as being more like a fourth−generation language. think of EXISTS as resembling an if clause. because these approachesalgebra or calculusare used as the models for designing relational query languages. the algebra is prescriptive.

because such languages are easier to grasp. NULL To this point in our discussion of the relational model. described above. The AND truth table:
T T F ? F F F F ? ? F ?
T F ?
The OR truth table:
T F ?
39
. but they include some algebra−like features that let users tune the languages behavior. In other cases. not just two.required to bring that end about. Logically. they also give us a way to test the robustness of those languages. it is a symbol that marks that a given datum is not known. no relational query language is relationally complete. its value is neither TRUE nor FALSE. or could not remember it. To handle these situations. You should keep the rule of relational completeness in mind whenever you evaluate a new language or tool for interrogating relational databases. NULL does not equal any other value. That NULLs logical value is neither TRUE nor FALSE creates some special problems when you evaluate the result of an expression: you must provide for the fact that an expression yields three logical outcomes. the given item of information does not apply to the entity that the row describes. F indicates false.
Relational completeness
Most relational query languages are calculus−based. for whatever reason. A language is said to be relationally complete if everything that can be expressed in the relational calculus can be expressed in that language without having to use a loop. As discussed in Chapter 3. a language is relationally complete if it implements Codds eight basic algebraic operators. Because relational calculus and relational algebra are models for relational query languages. Sometimes. Because the relational calculus and the relational algebra are equivalent. regardless of whether the expression evaluates to TRUE or FALSE. nor does it equal the outcome of any expression. and ? indicates NULL. we have assumed that every attribute of every row is populated with a member of the domain that that attribute represents. we run into situations where. the value of an attribute is not known. SQL is such a hybrid. That a relational expression can yield any of three possible logical outcomes means that the relational model uses a three−tiered logic. Note that T indicates true. however. The truth tables for the relational models three−tiered logic follow. Rather. Some come closer than others. To our knowledge. the data are missing due to error or human failing: a person did not type the information into the system.
Three−tiered logic
By design. the relational model introduces the notion of NULL. Sometimes. NULL is not a value.

this can create difficulties.
The great NULL controversy
The NULL has both costs and benefits associated with it. then neither expression
if (X == Y)
nor expression
if (X != Y)
is TRUE. we do not receive a meaningful valuesuch a comparison always yields NULL. the three−tiered logic creates certain problems for programmers. it gives you a third value for which you must explicitly check when you examine the logical value returned by an expression.
Keys and NULL
As we noted earlier. relations use primary and foreign keys. SQL has a special operation for performing logical comparison (see Chapter 3). not just two. To handle this situation. when we compare NULL with any value. Using NULL in a key will violate database integrity. Although it may not be clear from the truth tables. Furthermore. In particular. if X is TRUE and Y is NULL. NULL gives the relational model a way to permit an attribute to have missing values or forbid it from having them. rather. including NULL. NULL does not equate with any value. The definition of key requires that we compare attributes to determine whether they are the same. • The cost of NULL is mainly that programmers must write code to cope with the fact that an expression can have three logical results. NULL cannot be inserted into any attribute that comprises part of any primary or secondary key. As normal coding procedures usually assume that an expression is either TRUE or FALSE. each returns NULL. For this reason.
40
. However. We discuss database integrity at greater length later in this chapter. A foreign key is a combination of one or more attributes that uniquely identifies one or more rows within another relation. NULL offers the benefit of a standard way to handle missing values. A primary key is any combination of attributes that uniquely identifies each row within the relation. For example. • On the plus side. nor can it be greater or lesser than any value: any comparison with a variable that is NULL always yields NULLincluding comparing NULL with NULL.T F ?
T T T
T F ?
T ? ?
The NOT truth table:
T F F T ? ?
As you can see.

who are the two most important expositors of the relational database. This will become clearer as we begin to program databases. we have been working with relations that are staticalthough we have extracted data from relations. who invented the relational model. and that NULLs wreck the relational model. It especially comes into play when we are adding rows to a database or deleting rows from it. one must confirm that each foreign key within that row references a row that exists. Each is discussed in turn. This restriction is easy to understand. however. we have not inserted rows into them. and realize that they will complicate your work. To this point.C. but not so easy to enforce. database integrity means that every foreign key points to at least one existing row. you should handle them carefully. how data comprise relations. and how relations can be compared and modified to form new relations. He also suggests that the need for nullity indicates poor database design. Integrity has three aspects: database integrity. however. F. On the other hand. domain integrity. For example. NULLs are a fact of life. Database integrity In a nutshell. and for many tasks there simply is no practical substitution. Codd. it is unclear what our position should be. for data that cannot be known because they describe nonexistent entities. we have seen what data are. the appropriate NULL.
Additions
When a row is added to a relation. Our opinion is that NULLs are useful. for information that we can know about a subject but just dont know. Codd. have exactly opposite views on the NULL. Date and E. inappropriate NULL. and transaction integrity. a database should use a special value that lies within the domainalthough the tone of his writing suggests that he is uncomfortable with this suggestion. we encounter what is perhaps the most important problem in programming a relational database: maintaining the integrity of the database.
Relational integrity
At this point. Date suggests that to indicate nullity. Codds most recent writings describe two types of NULLone. J. After we begin to do so. no law says that a database you write must use them. states that the NULL is an inherent part of the relational model. However. consider again our relations BBTEAMS
<TEAM:MLBT> Braves Cubs White Sox Brewers <HS:STAD> Fulton County Stadium Wrigley Field Comiskey Park Milwaukee County Stadium
41
. and the other. nor have we removed rows from them or modified rows within them. Date states unequivocally that NULL is wrong. When faced with such strongly differing opinions from such respected authorities.

the deletion of rows is. If you are not careful. in others. • Does not change a value that is referenced by a foreign key. It just goes to show that in a tightly designed relational database. This strategy also presents some interesting problems if two rows reference each other and you attempt to delete one of them. There are three strategies for handling this situation: • The first strategy is to refuse to delete a row if another row references it through a foreign key. the correct response is to throw the row away and return an error message. This may be an error or it may simply be part of a wave of changes that you make to your database. This is always an error. the proper response is to cascade the change 42
. there must be a value for attribute BBTEAMS:TEAM that exactly matches the value for attribute GAMES:HT. The problem is to ensure that when you remove a row. • The third strategy is to modify the keys that reference the row being deleted. so that they point to another rowperhaps one that holds a default value. or you can wind up with rows whose foreign keys are meaningless. This is safer than the second strategy.
Updates
When you update a row.
Deletions
Database integrity can be a major issue when you attempt to delete rows from a relation. then we must ensure that for every row that we insert into GAMES.Mariners Angels
Kingdome Anaheim Stadium
and GAMES:
<HT:MLBT> Braves White Sox Angels Angels <VT:MLBT> Cubs Brewers Mariners Mariners <HT−RUNS:BR> 3 2 2 6 <VT−RUNS:BR> 5 8 1 7 <DG:GDAT> 05/05/95 05/05/95 05/05/95 05/05/95 <GNUM:NUM> 1 1 1 2
It is reasonable to make attribute GAMES:HT a foreign key for attribute BBTEAMS:TEAM. especially if the rows that reference the row being deleted themselves are referenced by still more rows. After we have done so. Now. a problematic action. a relation that included the name of the stadium in which the game was played. the question arises: what to do if inserting a given row were to violate database integrity? In most instances. Please note that the relational model dictates that database integrity must be maintained. each of these strategies has its problems. this strategy will blow a huge hole into your database. After all. The relational model does not dictate the strategy to use. • The second strategy is to remove all rows that reference the original row. but it does not indicate how it is to be maintained. Thus. but it must be done carefully. you must ensure that the modification: • Does not change a foreign key so that it references a nonexistent row. in some instances the proper response is to refuse to make the change. with the greatest of ease. you do not orphan other rows whose foreign keys reference the row being removed. at best. that would let us build. As you can see. if we wished. This strategy has obvious problems.

Another term for domain integrity is semantic integrity (from the Greek word for meaning). you must determine whether the change is an error. • The value of A limits the possible values of B. The word semantic pops up in the academic literature in many different combinationsfor example. a transaction guarantees that a partial order will not be entered: either all the records in an order will be written into the database.through the database. which you can use to enforce some rules. If you discover an error. you can roll back the modifications made since the beginning of the transaction: it will be as if they never occurred. These methods are not part of the relational model per se. B must also occur. we introduce them here because you will encounter them throughout your work with relational databases. For example. However. Some relational database management systems implement triggers. You will find that much of the work of designing and implementing a database involves articulating and coding the rules with which you will enforce the semantic integrity of your database. but they are bound to each other by the nature of the entity or event that each describes in part. or none are. • If A occurs. The following gives some of the commoner types of rules: • If A occurs. the relational model does not address the issue of semantic−level integrity. if deletion of a row causes a cascade of deletions of other rows that reference itthose side effects are undone as well. B cannot occur. and does its best to enforce them. for the most part the enforcement of rules is up to you. a rule−based system is one that is based in part upon a programmers articulation of semantic−level restrictions. however. Domain integrity Domain integrity refers to the fact that although some attributes are not bound to each other logically. 43
. A well−designed database system articulates such rules. With transactions. they all are applied to the database simultaneously. if an order−entry system writes multiple records into the database for each order. or none are applied to the database. or even be part of the same relation. and if the modifications happen. That is. either all modifications are made to the database. the attributes may not necessarily reference each other as keys. If a modification has side effectsfor example. they are bound to each other in the real world. thus. semantic restrictions or semantic−level integritybut all refer to restrictions derived from the meaning of the entity or event being described. The transaction either all of an order will be written into the database. Rule is also used for a semantic−level restriction. or none of them will be. Methods of enforcing integrity Relational database management systems have implemented a number of methods to help enforce integrity. In either case.
Transactions
A transaction treats a series of modifications to the database as though it were one modification: either all of the modifications to the database succeed. and do so based in part on domain−level considerations. or none of it will be. which leads us to our next topicdomain integrity. However.

for example.
A database index. you may wish to build an index for attribute HT. Most query languages implement some features of a true programming language. Java. however. as the databases implementer. most query languages let you perform arithmetic and declare variables. Cross Reference We discuss the art of indexing at greater length in Chapter 4. However. or Perl) to implement such features as input/output (I/O) or loops. Some persons argue that SQL itself falls into this category. based in large part upon a profile of how your database is used. must be able to implement the eight basic relational operations that we described earlier. In particular. complete model for our databases. Codds 12 rules of relational databases The relational model gives us a proven. many query languages depend upon a wrapper language (such as C. For example. in our GAMES relation described above. A relational query language does not have to implement many of the features commonly associated with a programming language. certainly. after an appropriate number of modifications have taken place. Many relational−database languages have been created. Other complications arise from the fact that some early implementations of the relational model cut corners in some ways. However. translating this model into bits that you can install and run on your Linux system is challenging. but they can also consume a great deal of processing time and disk space. it is up to you.The transaction mechanism is helpful. quick way to find the physical location of a given piece of information. which is introduced in Chapter 3. to determine what comprises a transaction. gives you an orderly. Indexes are very useful. You must. you must test whether the result is correct or not. These have affected the development of relational databases. by hand.
44
. and then either commit the modifications to the database. or roll them back. This would let you quickly look up all the rows for which a given team was at home. the most popular is Structured Query Language (SQL). Some complications arise from the fact that aspects of the relational model are difficult to implement. Thus. the devising of a set of indexes for your database is something of a black art. in the section on relational algebra. and may well have stunted them. then. Such a language. and the bottlenecks therein. it uses the index to enforce the rule that forbids duplicate rows within a relation. some features of SQL (such as the fact that it permits a table to hold duplicate rows) are definitely nonrelational. when we introduce SQL. We mention indexing here because SQL uses indexes to enforce some integrity rules. to be relationally complete. begin the transaction. like the index of a book. The relational model mandates the existence of a query language with which a person can establish and manipulate relations and rows.
Query language One last aspect of the relational model remains to be discussed: the query language. Cross Reference
Indexing
We will discuss transactions at greater length in Chapter 3.

and granting permissions to other users. and delete sets of rowsnot just one row at a time. Codd does not mandate a specific query language. The catalogue names the relations. Given his well−articulated distaste for SQL. The databases catalogue is itself stored within one or more relations that can be read by authorized users. creating or destroying relations. This is one feature of the relational database that sets it apart from other types of databases.Other complications arise from the fact that people have an enormous investment in existing technology. a part of the relational model. creating. Its contents can be read by users who have appropriate permission. the code with which a view is generatedwithin the database itself. 6. and keys that comprise the database. a relational database? In 1985. This language lets a user: ♦ Define a relation. 3. This is self−explanatory. some major. 4. No database management system fulfills all 12 criteria. Many database management systems also can hold viewsor rather. We will describe permissions in more detail in the next chapter. without having to go through the overhead of defining. This is the first commandment of relational databases. regardless of how good the alternative isif you have bought a lemon and cant afford to junk it. and using three−tiered logic. In brief. ♦ Bundle manipulations of the database as a transaction. ♦ Define views. NULL values are implemented systematically. The following paraphrases Codds 12 criteria. The system must be able to insert. Every datum can be accessed through the combination of the name of its relation. we discuss this further later in this chapter. Given that there is a gap between the ideal of the relational model and the reality of the implemented database. The database stores all data within rows. as a value that differs from every other value within the attributes domain. This rule of Codds introduces the notion of permissions. update. 8. because they permit a user to assemble data for viewing. The NULL must be implemented as described abovethat is. and that they simply cannot throw it away. but the criteria do give us a rule of thumb with which we can judge the degree to which a database management system fulfills the relational model. These tasks can include creating a database. permissions means that certain database tasks are restricted to selected users. thus permitting users to select and build views as they work. although usually there are some differences from platform to platformsome minor. The system implements a query language. The system must be able to update through a view. Most database management systems strive to fulfill this mandate. you just have to drive it. A view is a temporary relation that exists only to make data available for viewing. in order to interrogate the database and manipulate its contents. E. Views can be quite convenient. and populating a fully featured relation. 2. Codd certainly does not mandate that a relational database management system must implement SQLeven though SQL is supported by most commercial packages that claim to be relational. strictly speaking. F. ♦ Grant and remove permission to view or manipulate a relation. which is not. 9. the name of its attribute. attributes. and comments upon them: 1. 7. a relational database should appear the same and behave the same across all computer platforms. 5. The programs with which the database is manipulated are independent of how the database is physically stored or accessed. in fact. how can we judge whether a database that claims to be relational is. and the value of its rows primary key. ♦ Manipulate data. ♦ Set constraints to enforce database integrity. the rule from which all others flow. In other words. Codd published 12 criteria with which you can judge whether a given database system is truly relational. This rule mandates that rows be viewed as elements of a set. The programs with which the database is manipulated are independent of how the database is 45
.

sockets. Each of those machines is built out of smaller machines. No one can use a low−level language to subvert the databases integrity rules.
Hierarchic and Network Databases
Today. This does not apply to the definition of the databases relations. and other parts. in turn. the motherboard has a microprocessor. appearing in the early 1960s. a programmer should be able to code semantic integrity directly into the database itself. we discuss two older designs for databases: hierarchic databases and network databases. a machine can be comprised of many parts. In the bill of materials. firmware. and in part a way of slowing down the corruption of the database through shortcuts implemented by well−intentioned programmers. and various peripheral cards. Again. as it becomes common to distribute a single database over a network of machines. we discuss two designs that claim to be successors to the relational database: the object database and the object− relational database. Each of those parts. the relational model is the principal database tool. most database management systems strive to fulfill this mandate.
The hierarchic database
Modern machines often are built not out of simple parts. and be enforceable by the database management system itself. for example. This rule is a key to slowing the effects that the law of entropy inevitably will wreak upon your database. To our knowledge. This is in part a security measure. a 46
. and these component machines are themselves built out of other machines. For example. heads. simpler machines. whereas others claim to be successors. To manage the building of a machine as complex as a computer. Codds rules comprise a scorecard for relational databases: the more a package fulfills the letter of these rules. 11. but a given part can be installed only into one machine. controller board. In the following section. and each of those parts can have its own bill of materials. In other words. motor. until the components cannot be broken down (or decomposed) any further. but from other. instead of having to write customized code to enforce semantic rules. a keyboard. this rule mandates that code should survive upgrades to DBMS software. but not all succeed completely. Rules that articulate semantic−level integrity should be describable within the database management systems query language. but other database designs are also in use: some preceded the relational model. 10. The bill of materials lists all of the components that comprise the machine to be shipped. from the fully assembled computer down to the smallest nut and screw within it. a monitor. It was the first commercially successful electronic database. your personal computer is built out of a motherboard. In this section. the closer it adheres to the relational model. and therefore the more robust it is. In a hierarchic database. disk drives. A relational database should operate exactly the same whether housed on a single machine or distributed over a network. while a hard−disk drive consists of platters. has its own bill of materials that list its own parts. The hierarchic database models the bill of materials in software. In other words. This rule is becoming ever more important. and is still widely used today in mainframe shops. memory assemblies. be storable within the database systems catalogues. everyone must use the high−level languagewith its built−in rules and integrity measuresto manipulate the database. no commercial relational database management system implements this rule. Among other things.logically organized internally. cache chips. and other parts. The hierarchic database is so named because relations are arranged hierarchically. When taken together. manufacturers use a form called a bill of materials. glue chips. but it does apply to how the database management system implements those relations. 12. the bills of materials form a hierarchy that describe the machine. except in a rudimentary way.

A hierarchic database has many advantages: it is easy to implement. which owns the relation. If a machine has only one hard disk drive. another type of database entered the marketplace: the network database.
Object Databases
To this point. with static space allocated for a finite number of child records. Early object−oriented practice often tended to ignore formal database methodology by focusing instead on the persistence of individual. However. the network database permits a relation to have multiple parents as well as multiple children. in turn. For example. and to an indefinite number of child relations that it owns in turn. It is also worth noting that both the hierarchic and network systems were written for programmers rather than for users. the hierarchic design proves to be a limitation rather than a help. we introduce another type of database: the object database. As you see. it is inflexible: once a database is established. A network database can traverse the database by moving from salesperson to order. the entire hierarchy of data is crowded into a single huge record. Such a system is quite useful in specialized situations. and usually has a very fast access time. to solve some of the limitations of the hierarchic database. and so onmuch as a datagram bounces through a network. Each order record.relation points to exactly one parent relation. Object−oriented technology 47
. More often than not. A child is addressed as an offset in bytes within the record. for example. Often. easily understood structure. a hierarchic record that describes a computer may allocate space for exactly two hard disk drives. It is also fast and is easy to work with. each of which records an order that that salesperson took. is alien to the vocabulary of hierarchic systems. a sales system. Consider. This change brought major modifications to the very idea of data storage. if the machine has more than two hard disk drives. one for the person who purchased the item. In brief. we have discussed relational databases and relational theory. In the early 1990s. A record for a salesperson is linked to multiple child records. The term relation. In this section. Interrogating either database in most instances requires writing a custom program in a middle−level language. Its chief limitation is that few of the entities that people wish to model in a database decompose neatly into a hierarchic structure. However. in which the bill of materials exactly describes the entity that the database models. the space for the second is allocated but is left empty. and we have briefly discussed hierarchic and network databases. but is inflexible. The network database lets a programmer build a more data structure that is more complex than what can be built with a hierarchic database. modifying it is extremely difficult. can be linked to other parentssay. it also shares the limitations of the hierarchic system. and another for the item purchased. rather than being a key to another record. small−scale program objects to files. as we defined it earlier. such as manufacturing. some data are lost. such a system can be designed and implemented easily. The notion of an ad hoc query through an interpreted query language often is alien to these systems. the hierarchic database also has a number of significant limitations. object−oriented technology took over from the procedural model as the industrys preferred model for new software development. This design came about. in part. then from order either to the next order that that salesperson took or up to the person who placed the order. has a simple.
The network database
In 1971. In particular.

}
48
. polymorphism. boolean paySalary(). In OODBMSs (object−oriented database management systems). which are almost entirely alien to relational databases. attribute string name. For instance. normalization makes databases conform more closely to relational theory. the less readily it corresponds to an object model. In addition. In addition. attribute date birthday. in brief. taking advantage of capabilities such as polymorphism. they tend to reduce the normalization of the database in order to better match the object design. direct traversal of object relationships is a common form of query. and thus makes them more efficient and easy to manage. and Smalltalk. The first approaches to integrating object programming with relational databases involved encapsulating relational queries into object methods and messages. which can sometimes work against the strengths of relational databases. and must often make translations between the two in order to perform basic tasks. C++. This reduces performance to some extent. as object−oriented technology became a greater part of an organizations software infrastructure. In the case of object−oriented code connecting to RDBMS. the need to integrate into legacy data became more urgent.actually allowed some great advances in database integration. For instance.
The impedance mismatch problem
An impedance mismatch is a fundamental difference in the modeling of the same data in different parts of a system. often show very different behavior in another. The state of the art had been developing independently in the industry until the Object Database Management Group (ODMG) emerged with standards for data definition and querying. optimizations and algorithms that are simple or effective in one model. along with the combinatorial queries at the heart of RDBMSs. This means that programmers must master the two approaches. But problems were introduced by the object revolution.0. providing bindings for Java. This is not as simple as it might appear because just as object−oriented design introduced complexities to programming. Here is an example of ODL for an object that describes employees:
class Employee { attribute int id. complicating the tuning and development of applications. object−oriented design tends to access data by direct traversal of relationships between objects. it added a new dimension to databases. a key component of the impedance mismatch is that the more highly normalized the database. attribute Department dept. We will discuss normalization in a later chapter. When designers develop RDBMS and object−oriented systems in parallel.
Storing objects as they are programmed
The solution was to develop a database theory and practice that corresponds to the object−oriented model. which enables objects of different properties to respond in an intelligent way to the same message. offers an object definition language (ODL) and an object query language (OQL). but this exposed difficulties that have come to be known as an impedance mismatch. The current version of the standards. using object stubs that automatically update themselves from databases when their data is described. Relational technology had invested many years of research into scalability and simple object persistence did not benefit from such knowledge. enables programmers to completely hide the details of database storage in novel ways. and complicates the programming. ODMG 2.

an object is treated as persistent if it is created or handled within a database transaction. Department. The mechanism by which objects are determined to be persistent or transient differs from language to language. which contains the object class Order_Item { // String SKU. Objects that are meant to be kept in the database are called persistent.A class is the object database representation of an entity. So. }
Interestingly. Order_Item Item. but in most cases.city from Employee where name = "Carla Wong"
This OQL query might at first seem similar to the equivalent SQL query. In this case. in which all tables involved in the query had to be analyzed. Decimal Unit_Price. The from clause only includes the Employee extent. but the subtle difference is key. attribute string city. An attribute is the equivalent of a column of data. isolating the matching instances (one in this case). Then the query is completed by following a "path" from the instance to the instance referred to by its department attribute. let us assume that we have created Employee and Department objects in our favorite language. You will immediately see one difference in object−oriented databases. We discuss paySalary() in a moment.
49
. The programmer is expected to just create objects as usual in the language of choice. the query engine can evaluate the predicate where name = "Carla Wong" by only examining the Employee extent. In some languages. OODBMSs are optimized so that evaluating path expressions is very efficient. attribute string name. Traversing this relationship directly produces a reference to the Department instance. Accordingly. such expressions in OQL queries are known as "path" expressions. and all other objects are called transient. is clearly and directly expressed in the relevant attribute. which enables many types of queries to avoid combinatorial complexity. // }. We could determine Carla Wongs location by the following OQL:
select dept. to the city attribute of that department instance. which is the term for all object instances that are members of the Employee class. and the types are similar until we get to the dept attribute. relationship Employee heads inverse Employee::is_head_of. OODBMS does not provide a universal mechanism for adding in instances to these classes. Listing 2−1: Object Query Language Path Expressions
Given: class Order_Line { // String item_description. This eliminates the combinatorial problem we ran into in SQL. and the OODBMS engine will take care of storing and manipulating certain objects in the database. all objects in a particular class are persistent. because they follow a logical path from object attribute to attribute.
class Department { attribute int id. This comes from the keen desire for integration into object−oriented programming. Listing 2−1 illustrates a conceptual view of this process. The relationship with a different class. but first let us look at the ODL definition of Department. Employee Buyer.

inheritance of classes.
50
. there are very few OODBMSs. and have not gained a great deal of market acceptance. This is mainly because OODBMSs are difficult to implement. The details of ORDBMS differ from product to product. it involves providing features such as classes as a specialization of tables. For example. and an instance of a single order line Order_Line Line. the choices are even fewer. have developed a compromise between the two models: object−relational database management system (ORDBMS). and easily developed. // }. The object−oriented database is a good choice when you will be handling very complex types of data. Under Linux. Because there is no practical limit on the number of relations you can add to a database. There is also 4ODS. such as Zope for Python. you should match the database with the requirements of your task. When properly implemented. robust. Python even has an advanced nonpersistent object store in Gadfly. The relational database lets you build complex models out of small relations that you hooked together through foreign keys. The object−oriented database shines when users use these data interactively over a network. you expect a high volume of processing. or to the number of ways that you can hook those relations together. ORDBMS has proven very popular in the marketplace. and manufacturing systems all are well suited to hierarchic or network databases. recognizing the great advantages of OODBMSs. such as graphics or sound bites. but in general. while protecting their investment in legacy systems. payroll systems. There are several object−persistence engines that dont provide full−blown OODBMS capabilities. // }. ORDBMS enables organizations to migrate gradually to object systems. and you expect the structure of your data to change infrequently.Buyer.Decimal Unit_Cost. sales systems.
Choosing a Type of Database
When you choose the type of database to work with. an OODBMS wrapper for relational databases. these systems are fast. developed by FourThought LLC. which contains the object class Employee{ // String Name. The chief advantage of the relational database is its flexibility. especially when compared to the huge number of relational DBMSs. you can use the relational model to model an extremely complex entity or event. The hierarchic and network databases can be a good choice when your data have a hierarchic structure.Order_Item. especially when the queries that users will perform on the database are well defined. where one author works. The path expression for the name of the buyer for a given item is given by: Line. We hope that there will be more OODBMS options soon to match the variety of object−oriented tools available for Linux users. and more powerful relationships between classes.
The object−relational compromise
Many RDBMSs.Name
Unfortunately.

the effect on the database can also be positive. The user can use all of the databases attributes to build queriesthe user is not limited to the queries that the database programmer built into the database.
Client−server
For a variety of reasons. Originally. most database applications were on mainframes and the database and the application sat together. Users can ask questions of the database that were never imagined when the database was designed. We have already seen how connecting a relational database to object−oriented code can cause impedance mismatch. the relational model does not limit a users queries to predefined paths. This feature alone makes the relational database extremely valuable to business and science. and usage patterns of databases are all dependent on the application architecture that is employed. Until quite recently. and with it came a major new approach to databases: client−server. The structure. But its important to remember that databases are only part of an application. The software industry has moved through several phases in which various architectures were prevalent. and the user machine was a dumb terminal that displayed a basic form generated by the application on the remote mainframe. each a PC on a users desk. Figure 2−1 illustrates the client−server architecture. query engine. design. Finally. or as you learn more about the entitythe more you should consider using a relational database. Thus. the flexibility of the relational database means that it can withstand change more easily than can the other designs of database. The server is typically a very high−performance computer hosting the data store.The relational model lets you graft new relations onto a database without disturbing the relations that are already within the database (except for considerations of relational integrity). which host full−blown application code that connects to the server over the network. By aligning the database design more closely to the immediate needs of other parts of the application. There are then multiple clients.
Application Architectures
Databases can be so complex and resource−intensive that they appear almost an end in themselves. personal computer workstations gained great popularity in business. The bottom line is that the more complex the entity is that you are modeling. and the more that you expect your model to change over timeeither as the entity itself grows and changes. most databases were designed for the client−server model. and perhaps administration tools. communicating through message protocols.
51
.

many business applications separated the display routines from the core logic.Figure 2−1: Client−server architecture The client always has the code to display the application interface to the user. As object−oriented technology emerged and. developers began to attend more to design issues. The database server handles the raw data storage. causing excessive maintenance costs. low−level processing tasks to the server. and vice versa. A typical approach is that the client code involves much of the logic of the application. This was no new theoretical insight: the basic computer science goals of coupling and cohesion should have forbidden display and logic from being too tightly interwoven. developers often migrate routine. a great deal of application logic code would often be affected. especially when they are highly coupled to the persistent data.
Three−tier architecture
Developers discovered that having the display code tightly coupled to the application logic was problematic. processing the raw data according to the users requests and the business rules.
52
. the division of labor is fuzzy. coincidentally. When the display layout needed to be changed. The client manages data coming in from other sources such as real−time data. bringing about the three−tier architecture (see Figure 2−2). As stored procedures become more prevalent and more mature. and collaborates with code libraries and third−party modules. Beyond that.

order quantity. and a customer number. a middle−tier object (or combination of objects) could take as its inputs a product identifier (SKU). So. then the back end includes at least the Sales database and the Product and Inventory database. Cost of Sales. date. deduct the available stock from the Inventory Database. These servers are the source of the raw data that is eventually presented to the user.
53
. Overhead Expense. may be sent to the front end. and so on. If. which. For example. it is common to have a specific business rule for determining what profitability actually is. the data will most likely come from two databases. The back end is where we conceptually place the database server(s). The actual databases that make up the back end are dependent on the application that is running on the front end. The middle tier contains core application logic. In modern practice. one having the sales data. To illustrate the components of a multitier application using a database as the source of the information. and one having the product and inventory data.Figure 2−2: Three−tier architecture The user−interface layer contains the display and user input routines. Manufacturing Cost. It could then create queries to send to the back−end databases to record the sales amount in the Sales database. However. From this data. make an entry for the customer order in the Order Entry database. and sales region. for example. for an order−entry application. and creating database queries (SQL statements) as a result of the user actions on the front end and sending those queries to the back−end database(s). but the important processes basically fall into one of two classes: applying business rules to the data coming from the back−end databases as the data is passed to the front end. the user wishes to view sales revenue information along with product description information. As another example. and the like. In this case. we use the three−tier model. what happens in the middle tier? There are numerous tasks that occur. and so this model is sometimes called the N−tier model. the middle tier is often subdivided according to the needs of the particular application. both sources are part of the back end. It then manipulates this data according to predefined rules in order to provide a consistent value for profitability as its output. in turn. These processes usually work cooperatively in the middle tier. If the user is performing order−entry tasks. it is beneficial to have a processing component (often called an object) in the middle tier that takes as its inputs a product identifier (SKU). it creates and sends queries to the back−end databases to get values for Gross Revenue.

many of which are especially relevant to open−source databases. a number of databases. The data that is stored in the back−end databases is the content that interests us. We discuss this increasingly common configuration in−depth in Chapter 12. This was especially so in the database world. well just pretend that these data sources are implemented as databases. This implies that the middle tier has a database to store your customizations of the default home page (a customized home page is no more than a custom configuration of a set of standard page features). in which vendors tried to lock−in customers to their own proprietary features to ensure a predictable market base. So. However. 5. The emergence of Web technologies has brought about a variation of the three−tier model. or the data is sold. developer and end−user demand has produced an atmosphere in which vendors are under pressure to create and follow industrywide standards. one could replace one or more of the back−end databases with those of another vendor and not have to change anything whatsoever in either the front end or in any of the middle−tier objects. fractious. Because this book is about Linux and databases. and it is only recently that DBMS vendors have dedicated themselves to SQL compliance.
Modern Advancements
Recent developments in database and application technology have brought about many fundamental changes in databases. a default Web page is created and presented. Present a log−in page (it could be a couple of edit boxes on a public HTML page) so that your access privileges can be verified and security can be maintained. This is suggested as the preferred method over cookies in which the data to be accessed has any combination of privacy requirements. its worthwhile to point out the similarities of the browser/Web server combination to the three−tier model discussed by way of an example of a Web portal. we have a presentation layer (the user interface or front end) that is implemented using a Web browser inherently browsing HTML files. The purpose of the middle layer then is to format the information coming from the data source(s) as HTML documents and present them to your Web browser. Beginning with the three−tier model. The same can be said (in theory!) for the front end and middle−tier objects. in this case. retrieve the customizations that were previously created. Verify the log−in username and password in a portal security database. 4. So. which returns the results of one or more SQL queries. At the back end are our information sources. is proprietary. 2. and very political process. Organizations that used different database products in different departments or for different applications often found themselves with serious maintenance and interoperability problems. the resulting HTML document is presented to you as your custom home page. Fortunately.In theory.
The era of open standards
It used to be in the software industry that every meaningful standard was a de facto market triumph for a particular vendor. the end user. to a great extent the back end of our model should consist of generic data sources. 3. Technologies such as XML (eXtensible Markup Language) and Java have been driven 54
. SQL continues to develop. After all of the configurable components of your home page are processed. which variation is suited to the browser/Web server combination. the middle−tier components need to: 1. Each result set is formatted for presentation and inserted into the HTML document (your custom home page). If no personalization exits. and standards have emerged for object databases. to successfully view and use the data stored on the back−end database servers. The emergence of open database standards such as SQL was a long. After verification of the username and password. Processing each parameterized custom URL in turn. the server sends each parameterized URL to the appropriate database server.

Open standards benefit everyone. PostgreSQL and MySQL implement ANSI SQL. including vendors. because it enables better searching. especially to database users. greatly slowing down the development process. a standard format for general documents and data. as well as Java Database Connectivity (JDBC). which is standardized by the IETF. it would be impossible to provide in−depth coverage of seven products in a single book. • Mozilla implements HTML and CSS (cascading style sheets). which is recommended specifications of the World Wide Web Consortium (W3C). by improving productivity and speeding up the development cycle. specialized software to be performed by off−the−shelf utilities. and to provide a means of transmitting structured data between software components. Without the standards in use in most Linux databases. OSS developers have a well−documented programming target. has gained a lot of media attention as an HTML replacement. • GNOME and KDE both use distributed programming tools. Many databases are moving to support XML. This latter application is known as serialization.by standards bodies from the beginning (although not without a great deal of politics. which is maintained by The Open Group. • XFree86 implements the X11 display standard. but it is far more than that. which is administered by ANSI. XMLs importance is in the fact that so many vendors and developers have embraced it as a data format. and they can concentrate on more interesting problems. With open standards. In the days of proprietary standards. especially in the Java arena). which is a standard of the OMG.
eXtensible markup language
XML. • Apache implements HTTP (hypertext transfer protocol). • Linux follows the POSIX standard for operating systems. and linking on the Internet. A possible XML serialization of the relational database we have been using in our examples is as follows:
<?xml version="1. and allows a lot of work that formerly needed custom. and are now transforming database technology and practice. Almost every successful OSS project has enjoyed the benefits of a core industry standard. both to enable users to store documents in a rich format within the database. This provides a great boost to interoperability between software components. based on CORBA (Common Object Request Broker Architecture). open−source solutions (OSS) developers often had to guess or reverse−engineer protocols for interoperability with commercial tools. • Of course.0"?> <Database> <Table name="Employee"> <Row> <Column name="id" type="int4">101</Column> <Column name="name" type="string">Manny Vegas</Column> <Column name="birthday" type="datetime"> 1950−05−10</Column> <Column name="dept" type="int4">12</Column> </Row> <Row> <Column name="id" type="int4">102</Column> <Column name="name" type="string">Carla Wong</Column> <Column name="birthday" type="datetime">1961−12−02</Column> <Column name="dept" type="int4">15</Column> </Row> <Row>
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. categorization. Open standards have also been good for that other recent phenomenon of openness: open source.

the developer must use a very different mechanism to manipulate native SQL data and BLOBsSQL queries in the former case. By using ORDBMS techniques. This approach has several problems. of groups of data that are related to one another. and ratio.
Summary
In this chapter. and updating data. An attribute is to a relation what a column is to a table. each of which is composed of one or more attributes. of which the most common are nominal. file calls in the latter case. When we work with a database. A row is to a relation what a row is to a table. A datum has a type. Maintaining data means performing four tasks with our body of data: inserting. not individual data. A database is not just a collection of random data. ordinal. extended data types can be organized into classes with specialized operations. a language is 57
. and that together describe an entity or event more or less completely. The calculus and the algebra are equivalentany statement in one can be transformed into an equivalent statement in the other. it consists of relationsthat is. an attribute defines a domains role within the relation. which are similar to BLOBS but consist of text data that makes searching and indexing easier. Each attribute has a name that is unique within the relation. interval. A datum is a symbol that describes an entity or event in the real world. it defines a view. Rather. The relational model has developed two systems for manipulating relations: relational algebra and relational calculus. It also means preserving the integrity of the data. we discussed what a database is. Stored procedures help a bit. One can then write database procedures that can intelligently query and manipulate BLOBs. Relational calculus is descriptivethat is. deleting. Each row holds exactly one value drawn from each attribute that comprises the relation. The relational model gives a theoretical model for databases. For instance. it describes operations that you can perform upon relations. It is also impossible to make intelligent queries of objects. a relation is a set of domains that together describe a given entity or event in the real world. A relation is comprised of attributes. Data within the relation are stored in the form of rows. Both the calculus and the algebra are the basis for query languages. or groups of related data. retrieving. Most of the Linux databases we discuss offer universal features in one form or another. The algebra is prescriptivethat is. without going into details as to how it is to be built.would provide a filelike interface to the object. to select all images that are photographs taken against a white background. Universal databases combine these various capabilities in order to allow a richer variety of data to be stored in databases. A database is an orderly body of data and the software that maintains it. we manipulate relations. Each row can be identified as unique by one or more primary keys. for instance. Caution Dont confuse our use of universal with the use of the same term by several database vendors to mean same features on all supported platforms. The meaning of a datum depends in large part upon the domain of which it is a member. Other extensions involve Character Large Objects (CLOBS). The relational model manipulates relations. which gives all possible values for the aspect of the entity or event that that datum describes. each of which identifies one or more rows in another relation. A row can also contain one or more foreign keys. A datum also belongs to a domain.

Next. E. which we discuss in coming chapters. There is a gap between the relational model in the abstract. We compared the relational database with hierarchic. and of the data they contain. New technologies and developments are constantly changing the database world. F. Codd defined 12 rules for gauging just how relational a relational database management system is. but most fall into the ORDBMS category. without loops. The relational model uses NULL to handle situations in which a value for an attribute is not known. There are many variations on these technologies in Linux databases. thus. with impossible being determined in part by other data within the relation. and its implementation as software. and object−oriented databases. NULL is neither TRUE nor FALSE.
58
. and Linux users are definitely a beneficiary of industry advancements.relationally complete if it can express. thus. Databases must guard the integrity of their structures. network. we discuss the classifications of data that you might need to manage with Linux DBMS and try to suggest a strategy based on your particular needs. any expression that can be expressed in the relational algebra. Data integrity means ensuring that data do not contain impossible values. NULL is guaranteed to be not equivalent to any value in any domain. comparing any value with NULL will always be false. Structural integrity ensures that every foreign key points to an existing row. statements in a relational language must be evaluated with a three−tier logic. Logically.

F. it attracted the interest of a number of database researchers. In 1986. which discusses the art and science of designing a database. IBMs power in the marketplace. Through the early years of the 1980s. To confuse matters.) Ingres QUEL language is well regarded among cognoscenti of relational databases. and it is supported by all of the major manufacturers of relational database management systems. IBM in effect declared the relational databaseand in particular SQLto be its standard for databases. although the SQL−based relational database products dwarf its popularity. about five years after Codds initial publication.
59
. Codd published his initial work on relational databases in 1969. SQL is by far the most popular query language for relational databases. which was much greater in the 1980s than it is today. the committee grappled with the question of just which relational query language should be used as the model for its standard. The following year. designed a relational database named Ingres that was built around a query language named QUEL. IBM formed its System/R project. Thus. In this chapter. as part of its design of a relational database. it is common for the string SQL to be pronounced sequelthus preserving a phonetic ghost of the languages original name. Sybase.Chapter 3: SQL
Chapter 2 discussed the theory of the relational database. This chapter introduces structured query language (SQL). In 1974. A commercial version of Ingres was built in 1981 and is still sold.
SQL standards
In 1982. ANSI bowed to reality and adopted SQL as its standard query language for relational databases. (Although this groups version of Ingres is no longer being supported or enhanced. Soon thereafter. ANSI and ISO have combined their efforts in this area.
Origins of SQL
When E. Oracle remains the largest selling relational database product on the market. This product was named Oracle. to this day. and Oracle. we begin to write code to implement databases. IBM introduced DB2. University Ingres is widely available for Linux for free. One group led by Professor Michael Stonebraker of the University of California. or Structured Query Language. the original Ingres project was continued by UC Berkeley through the 1980s. under the name University Ingres. Doing so prepares you for Chapter 4. IBM worked to make SQL the standard query language in the marketplace. Codds specification for a relational database mandated that a query language be created. and that this query language must be the only avenue by which data can be manipulated within the database. including a group at IBM. In 1983. the American National Standards Institute (ANSI) formed a committee to work on a standard for relational database query languages. its relational product for mainframe computers. at the same time. ensured that SQL became the de facto standard for relational databases throughout the computer market. but it has never enjoyed the acceptance that the market has bestowed upon SQL. later renamed SQL. a commercial venture was founded to create a commercial relational database that was modeled after IBMs relational database and SQL. the System/R project designed a query language that they named SEQUEL. (By the way. the International Organization for Standardization (ISO) adopted the ANSI standard as its standard for relational query languages. Berkeley.) System/R began its first customer tests in 1978. since then. including Informix. which was given the task of designing and building a prototype relational database system. As you recall. Other groups besides IBM were also exploring the relational database.

How an implementation of SQL behaves depends on a number of factors. In fairness. SQL can be quite clumsy. implementations of SQL have features that make them mutually exclusive.
60
. is the standard used today. Another problem is that SQL does not adhere strictly to the relational model. portability of SQL is largely a myth: only rarely will you be able to take a file of SQL code written for one relational database package and run it without modification under another relational database package. the standards mark some details as being implementor−specific. the advent of Microsofts Open Database Connectivity (ODBC) and similar protocols help to smooth over the differences between different implementations of SQL. Unfortunately. as a programming language. the language described in this standard is known as SQL1 or SQL−89. it will define how objects are to be handled within a relational database. these differences are slight.
Dialects of SQL
SQL. SQL permits duplicate rows within a relation. we pointed out a number of ways in which SQL and the relational model differ. This standard fixed a number of holes in the original standard. Unfortunately. We point out other places in this chapter where SQL departs from the relational model. Also. PostgreSQL offers many of the features of an object−relational database. and it is a good place to start an exploration of the object−relational database. Also. (Object databases and object−relational databases were discussed in Chapter 2. In Chapter 2. then the good news. in particular. In 1992. but also extended the language greatly. called SQL2 or SQL−92. ANSI/ISO published a new standard for SQL. Cross Reference We discuss ODBC and its relatives JDBC and Perl DBI in Chapters 12 and 13. SQL2 (1992 standard). or SQL2 plus extensions drawn from the draft SQL3 standard and the packageand vendor−specific extensions to the language. Well give you the bad news first. in particular.A revised edition of the ANSI/ISO standard was published in 1989.) SQL3 is beyond the scope of this book. we must emphasize that in most instances. Finally. however. obviously. This standard. like any standard language. Work is proceeding on a third standard for SQL. is that SQL is not one language.
Disadvantages and advantages of SQL
SQL does offer a number of advantages and disadvantages. but a family of languagesalbeit closely related languagesas shown in the preceding section. is meant to be uniform across all products. These include the ANSI/ISO standard supportedSQL1 (1989 standard). called (not surprisingly) SQL3. on all platforms. This new standard will again extend the language. and it can also be ambiguous. and porting a file of SQL code from one package to another usually is a straightforward job. Disadvantages The first problem.

the programmer writes a series of calls to execute SQL (CLI) statements. SQL call−level interface In this interface. as well as dump a copy of a databases contents into a text file. SQL was designed to work with a host language that provides facilities such as input/output and flow control. SQL as a language is relatively straightforward and easy to learn. which. to a business. Even nonprogrammers can learn to write their own queries and reports in it. Earlier interpreters received code typed by the user. nowadays. We explore ODBC and JDBC in Chapters 12 and 13. or schema. For the most part. such as C or COBOL. SQL statements are embedded within a program written in another language. For most packages. an interpreter is likelier to receive input from a graphical user interface. like C or Java. The preprocessors output is then compiled and run like any other program. 61 SQL interpreter
. each database manufacturer has invented its own CLI. by and large it implements the relational model faithfully. These omissions are not an error. Although SQL does depart from the relational model on a number of points. SQL places the power of the relational database into the hands of programmers and usersand we can think of no greater recommendation than that. SQL instructions can be passed to the engine in any of three ways: Such an interpreter receives input directly from the user. Rather. acts as the gatekeeper to the database: it executes instructions to set up a database. is a standard. or updates data within it. Some manufacturers have designed CLIs that can be used with nearly all relational databases. these include instructions for redirecting input or output flow−control statements. The ANSI/ISO standards for SQL define both interpreted and embedded SQL. in particular. it helps to unlock the data jail. Most relational database packages also include utilities that let you create a copy of a databases design. the calls are to the methods within a package of objects. which protects the user from having to write code. in Java. Such a program must first be filtered through a preprocessor. the programmer writes by hand the code that the embedded−SQL preprocessor generates mechanically. but it is available and can be quite useful. In effect. and these are mutually incompatible. is an advantage that cannot be underestimated.Advantages SQL. they do not define an SQL call−level interface for any other computer language. Most database packages use an SQL engine to interpret SQL instructions. database activity goes through the SQL engine. and load a file of data directly into a database. The engine is a program that. although it has problems. which transforms the embedded SQL into a series of function calls. It does not contain many of the features offered by a general−purpose programming language. however. Embedded SQL Here. This method of programming SQL is largely outdated and is not explored in this book.
Implementation of the language
SQL is a language designed to work with a database. Thus. and returns the output to the user. Microsofts ODBC protocol and Suns Java Database Connectivity (JDBC) protocol have attracted support in the marketplace. in effect. selects or deletes data from it. This helps to give ordinary users access to their own data within a databasein effect. the calls are to functions within a library. interprets it. inserts data into it. In C. however.

Note Please note that the term field often is used as a synonym for column. we look at the structure of SQLthe scaffolding that holds our statements together. gives different names to each: • Instead of relations. the information we present enables you to perform all of the tasks ordinarily required when you create and work with a relational database. column. Where the differences between relational entities and the SQL analogs affect our discussion. such as C.
Structure of the language
As we noted earlier. respectively. and tuple. without worrying about the logic of the program as a whole. and their analogs in SQL. however. and with fear of what it can do to you.
62
. Such features can be provided by the host language within which SQL statements are embedded. You should treat SQL with the care you give to any power tool: with respect for what it can do for you. we have used the terms relation. attribute. attribute. Our discussion is limited to the core features of the SQL2 standard. SQL speaks of tables. nor can it store data in variables for use by another statement. Before we begin exploring statements. we will use column and row exclusively.
Terminology
In our discussion of relational databases so far. learning SQL means learning the syntax of each SQL statement. or a column. However. You cannot use a keyword to name a database. and row. A carefully constructed SQL statement can perform an enormous amount of work very quickly. but such features are not part of SQL itself. it is correct to regard relation. We must emphasize that SQL is a powerful language. or about the side effects statements can have on each other. Thus. Each section presents examples written in SQL. SQL. We do not go into the more esoteric features of the language.SQL Structure
The rest of this chapter introduces SQL. and the term record is used as a synonym for row. there are some differences between the relational entities relation. and tuple. and what it does. however. • Instead of tuples. a table. a carelessly constructed SQL statement can destroy a database. Because SQL does not adhere perfectly to the relational model. or any other namable element in your SQL program. however. The statements within a SQL program are executed in isolation from each other: that is. SQL does not implement some of the features of a general−purpose programming language.
Keywords
SQL reserves words for its own useas keywords. SQL speaks of rows. SQL speaks of columns. However. for the sake of simplicity. • Instead of attributes. attribute. we identify those differences. and tuple as equivalent to table. a statement cannot invoke another statement. nor can it pass information to another statement. That is one reason why SQL is so easy for nonprogrammers to learna person can learn SQL statement by statement. We use the SQL terminology throughout the rest of this chapter. For the most part.

The following gives the most commonly used SQL keywords: ALL AND ANY AS ASC AUTHORIZATION AVG BEGIN BETWEEN BIT BY CHAR CHARACTER CHECK CLOSE COMMIT CONTINUE COUNT CREATE CURRENT CURSOR DEFAULT DATE DEC DECIMAL DECLARE DELETE DESC DISTINCT DOUBLE END ESCAPE EXEC EXISTS FETCH FLOAT FOR FOREIGN FOUND FROM GO GOTO GRANT GROUP HAVING INSERT IN INTO INDICATOR INTEGER INTERVAL IS KEY LANGUAGE LIKE MAX MIN MODULE MONEY NCHAR NOT NULL NUMERIC OF ON OPEN OPTION OR ORDER PRECISION PRIMARY PRIVILEGES PROCEDURE PUBLIC SCHEMA SECTION SELECT SET SMALLINT SOME SUM TABLE TIME TIMESTAMP TO UNION UNIQUE UPDATE USER REAL REFERENCES REVOKE ROLLBACK VALUES VARCHAR VARYING VIEW WHENEVER WHERE WITH WORK SQL code is case−insensitive: that is. SQLs data types dictate not only the varieties of data that a SQL program can manipulate. but this is not required. defines types of data. but the varieties that can be stored in a SQL database. It is customary to type SQL keywords in uppercase letters and to type table names and column names in lowercase.
Data Types
SQL. and chArActEr are all equivalent as far as SQL is concerned.SQL2 (that is. character. you will need only a handful in your day−to−day work with SQL. Of this vast number of keywords. SQL−92) reserves more than 300 keywords (as compared to 33 in ANSI C). and can (as its name implies) hold a defined type of datum. like all languages. The following sections introduce each keyword in its proper context. Each data type allocates a defined amount of memory. The following are the simple data types that are recognized by all implementations of SQL: CHAR(length) INTEGER Fixed−length array of characters Four−byte (long) integer 63
. CHARACTER.

Other. up to a maximum of 100. • The INTERVAL type records the interval between two timestamps. the database will store only the number of characters that you insert into the column. precision gives the position of the decimal point within the number. its usually used to timestamp an event that occurs right now. SQL allocates space for 100 characters.SMALLINT Two−byte (short) integer FLOAT Single−precision floating− point number These data types should be familiar to anyone who has programmed. but some database management systems offer them should you need them: BLOB BIT(length) BIT VARYING(length) NCHAR(length) NCHAR VARYING(length) SERIAL Binary large object Fixed−length array of bits Variable−length array of bits Fixed−length array of national characters Variable−length array of national characters Automatically generated serial number
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. The maximum length of a VARCHAR varies from one database package to another. The following data types are more complex than the simple types described above. scale) Synonym for NUMERIC DEC(precision. if you declare the column to be VARCHAR(100). for many. the maximum length is 255 characters. Not every implementation of SQL recognizes all of these data types. You will not use these types often. but most implementations recognize at least some of them: VARCHAR(length) Variable−length array of characters NUMERIC(precision. that require more precision than is allowed by an ordinary floating−point number. to a maximum of scale digits. Such numbers are used to store numbers that are too large to fit into a 32−bit integer. more exotic data types also are available. and so cannot easily be subtracted from another TIMESTAMP. Rather. • The TIMESTAMP type records both date and time in one column. or for which you wish to avoid rounding errors. scale) Synonym for NUMERIC DOUBLE PRECISION Double−precision floating−point number DATE A date TIME(precision) The time TIMESTAMP(precision) The current date and time INTERVAL The interval between two timestamps The complex data types extend the simple types in the following ways: • A variable−length array of characters is one whose length is not fixed. • The DATE and TIME types offer a convenient way to record dates and times. A double−precision number is used for tasks that require extremely fine precision. If you declare a column to be CHAR(100). it stores numbers as text. • A double−precision number is an 8−byte floating−point number that offers twice the precision of a single−precision FLOAT. regardless of whether you insert text into the column. • The NUMERIC data type does not encode numbers in the usual binary manner. scale) Decimal number DECIMAL(precision. However. Programmers may wish to note that SQL does not support unsigned data types. The precision of the timestamp can be set down to nanoseconds. using 1 byte for each digit in the number. This is needed because a TIMESTAMP is not an integer type.

The SERIAL type is used by the Informix database management system. In the rest of this chapter. That is because relational database packages differ in their definition of just what a database is. and creating tables and indices. and still other packages let the system administrator define databases when the system is installed. as you would expect. Unlike a true software object. The proliferation of such customized data types is one reason why it is difficult to port SQL code from one database package to another. In this section. size) Money MONEY Money BOOLEAN A Boolean value A binary large object is a binary object of indefinite size. whereas other packages define the entire package as one large database.S. each with its own complement of tables and indices. this is a character with a value from 128 to 255. The BOOLEAN holds a Boolean valueTRUE or FALSEand nothing else. Such an array can be used for a variety of specialized tasks. just like arrays of characters.MONEY(precision. we can begin working with SQL. The NCHAR types hold arrays of national characters. holds a sum of money. granting permissions to users. and throughout the rest of this chapter. Therefore. we discuss it. but not thereafter. When MySQL does something unorthodox. a picture or a sound bite. (MySQL uses the keyword AUTO_INCREMENT to do the same thing. or has a serious limitation. two−table database that we call baseball. This type holds a serial number that is generated by the database enginethat is. Note that not every implementation of this data type uses the arguments in parentheses. we present examples that run under MySQL. The first step is to create a database. the database engine automatically sets the value of this column to the next highest possible integer value. It is analogous to the NUMERIC data type.) The MONEY type. Many other vendor−specific data types are available. This is not the place to go into the details of running MySQLwe cover that in Chapter 10but the example scripts here do work with most popular database packages. This involves creating the database itself. Some packages let users define any number of databases. You will learn all about this database as we proceed through this chapter. usually.
Creating a Database
Now that we have discussed the data types that most SQL packages support. it may strike you as odd that SQL does not have an instruction for creating a database. Bit arrays can either be fixed length or variable length. all a BLOB contains is the data that comprise the object. because it holds data about baseball games. The bit types define an array of individual bits.
CREATE: Create a database
Much of this book to this point has been concerned with defining just what a database is. for example. a BLOB does not contain any methods for manipulating the object. we will work with a simple. ASCII set.
65
. in that it is designed to avoid rounding errors when you divide one sum of money by another. A national character is a character that does not appear in the U.

grants global permissions on the database baseball to user bballfan: Listing 3−2: Granting Permission
GRANT ALL ON baseball. The user can delete rows from the specified table. Other RDBMS packages use different characters to end a statement. The script in Listing 3−1. this GRANT statement tells MySQL to give all possible permissions on every table in the baseball database to user bballfan. and how to go about it. Database packages vary wildly in how they manage permissions. a database can be created only by the root user. The SQL instruction GRANT lets you grant permissions. Note. MySQL also implements the statement DROP DATABASE. however. to signal the interpreter mysql that the statement is ended and should be executed. whereas Sybase uses the command go.
Please note that under MySQL. the mini−SQL package mSQL uses the escape sequence \g. too. that the statement ends with a semicolon. who accesses the database on the local host (rather than from another host on your network). In brief. The script in Listing 3−2. and the permission scheme used by MySQL is particularly convoluted. for example.
We discuss the MySQL system of permissions at length in Chapter 10.* TO bballfan@localhost IDENTIFIED BY password. The types of permission that you can set vary from one database package to another. permissions on the database need to be granted so that users can access and work with the database. The user can insert new rows into the specified table. which lets you throw away an existing database. Most packages recognize these types of permission: CONNECT INSERT DELETE UPDATE The user can connect to the database. creates the baseball database under MySQL: Listing 3−1: Creating a Baseball Database
CREATE DATABASE baseball.
GRANT: Grant permissions
After the database is created. and whose database password is password. 66
. The user can modify rows within the specified table. or by a user to whom the root user has assigned database−creation privileges.Most database packages that let users define their own databases use a statement of the form:
CREATE DATABASE database_name
You should check the documentation that comes with the package you are using to determine what the package permits you to do in the way of setting up databases.

The optional name is followed by the names of the column or columns that comprise the foreign key. Clauses within the CREATE TABLE statement must be separated by a comma. require that a login used to access the database must also be a login used by the operating system. we discuss data types at greater length below. whereas Sybase assumes that a column can hold a NULL value unless you explicitly use the NOT NULL clause. ] ) ] [FOREIGN KEY [ key_name ] (column_name [ . The name is not necessary. • These are followed by the keyword REFERENCES and the name of the table to which this foreign key points. 67
. Now that we have created the database. MySQL assumes that a column cannot hold a NULL value unless you explicitly use the NULL clause. The optional PRIMARY KEY clause names the columns that comprise the tables primary key. declaring a primary key lets the database engine enforce this rule. column_name. It is a little more complex than the PRIMARY KEY clause: • The keywords FOREIGN KEY are followed by an optional name for the key. As you would expect. This statement has the following syntax:
CREATE TABLE table_name( column_name column_type[. these packages would require that bballfan be a Linux login as well as a database login. CREATE TABLE: Create a table The statement CREATE TABLE creates a table within a given database. Also. For example.Note that for MySQL. every row in the table must have a unique value for its primary key. This name must be unique within the table. can reference only a primary key. the next step is to build the tables that will actually hold data. Optional clause NULL states that the column can hold NULL values. The optional FOREIGN KEY clause defines a foreign key. bballfan does not have to be a Linux loginany user who knows the password can use that login to access database baseball. but you should name each key in case you later decide to drop it. If you do not explicitly state whether a column can hold a NULL value.] [NULL|NOT NULL] [PRIMARY KEY (column_name [ . column_name names a column. This name must be unique within the database. As you can see. This is an important point upon which SQL is not quite in sync with relational theory. REFERENCES table_name [ ON DELETE action ] ] )
] )
table_name names the table. which varies from one package to another. however. Other database packages. For example. Earlier in this chapter. under SQL. The SQL instruction REVOKE removes a permission that had been granted previously. a foreign key does not name the columns in the foreign table to which the foreign key points: this is because a foreign key. column_name. optional clause NOT NULL states that the column cannot hold NULL values. we described the data types that are used most commonly. the database package uses a default. SQL lets a table have only one primary key. when you declare a primary key for a table. SQL lets you declare foreign keys that point to it from other tables. The name or names are enclosed between parentheses. column_type assigns a data type to the column. Likewise.

visiting_team. visiting_team_runs SMALLINT NOT NULL. division CHAR(1) NOT NULL. note that MySQL does not let you name a FOREIGN KEY: if you do. ON DELETE accepts the following options: Automatically deletes every row that references the row that has just been deleted from the foreign table. Listing 3−3: Creating Tables for the Baseball Database
CREATE TABLE team ( team_name CHAR(15) NOT NULL. visiting_team CHAR(15) NOT NULL. To be declarable as a FOREIGN KEY. when we designed the relations upon which these tables are based. league CHAR(1) NOT NULL. who use brackets to enclose the size of an array. The script in Listing 3−3 shows how to create the tables for the baseball database under MySQL. it complains of a syntax 68
. In Chapter 2. which defines the action to take should the row that the foreign key references be deleted. PRIMARY KEY (home_team. SET NULL Sets the foreign−key column or columns to NULL. forbids the references row to be deleted. MySQL does not recognize the FOREIGN KEY clause. some databases (for example. FOREIGN KEY (home_team) REFERENCES team ). and to type the names of all columns and tables in lowercase letters. PRIMARY KEY (team_name) ). It is customary to type SQL keywords in uppercase letters. but cannot be done under SQL. the data types and domains of the columns that comprise the foreign key must exactly match those of the other tables primary key. however. game_number).Obviously. when we discussed the concept of database integrity. CREATE TABLE game ( home_team CHAR(15) NOT NULL.
CASCADE
The following points should be noted: • The size of an array is enclosed between parentheses. • The names of the tables are given in lowercase letters rather than in uppercase letters. You may recall that we discussed these options in Chapter 2. home_team_runs SMALLINT NOT NULL. Also. NO ACTION That is. stadium CHAR(30) NOT NULL. Although SQL is not case sensitive. game_number SMALLINT NOT NULL. we defined some foreign keys that refer to columns other than a primary key. This may be a little confusing to C programmers. it lets you insert one into a table definition both to document foreign keys and to maintain compatibility with standard SQL. This is optionally followed by the keywords ON DELETE. This is perfectly legal under relational theory. • Finally. game_date CHAR(10) NOT NULL. game_date. Sybase) are case sensitive as regards table names and column names. the key must point to the declared primary key of the table that that foreign key references. city CHAR(15) NOT NULL.

the name of a stateCalifornia). We used fixed−length arrays for the string columns. instead of VARCHAR types. we discussed the SQL data types that are most commonly used. with those codes interpreted by a key that we embed in the software. to hold such lengthy names as Hubert H. plus a couple of extra. respectively). static table like this one. The assigning of the data type to a column is an important issue that requires more than a little thought. Our counting the number in the names of baseball teams is a mundane example of one of the cardinal principles for assigning a data type: The data type you assign to a column must be physically able to hold every value of that columns domain.) This enables these columns to hold the longest team name (Metropolitansaka Mets) and the longest city name (actually. it should be one that is easily and accurately interpreted by most users. Central. mainly for the sake of simplicity. theres little point in using a VARCHAR type with a small. As you can see from the above example. After all. to put it another way: You cant jam a ten−pound domain into a five−pound data type. because this information can be represented as one character: the league can be flagged by the characters A and N (for American and National. That we assigned columns home_team and visiting_team the same data type as column team_name is an instance of another of the cardinal rules of assigning data types: When a column is a 69
. Assigning data types Earlier in this chapter. If we intended our database to be extended to minor leagues or to foreign leagues. unless you are intent on wringing every last superfluous byte out of your database.error. we briefly discuss why we assigned these data types to the columns in the baseball database. C. we can store the names of leagues and divisions as codes because they lend themselves to unique abbreviations that are universally understood by American baseball fans. he might think it meant the Pacific Coast League. (The data type CHAR is a synonym for CHARACTER. Our decision to use one−character codes to identify league and division raises an important question about how information should be stored within a column. and West. This table will have only 30 rows in itone for each major−league team. 1 to represent the American League. plus a couple of extra just for luck. then we would write out the names of leagues and divisions in full. 2 for the National Leaguethrough 99 for the Northern League). In this instance. an American minor league. Although we discuss this topic at length in Chapter 4. You will see this principle expressed repeatedly throughout this section. we made columns team_name and city each a 15−byte character array. respectively). But why bother? If were going to use a code. to help keep you from becoming utterly confused. Columns league and division are each one−character columns. or within another table. and the division by the characters E. theres no guarantee that an American baseball fan would recognize a P as representing the Japanese Pacific League.
Table team
In this table.
Table game
Columns home_team and visiting_team are 15−character text columns to match the type of column team_name in table team. Or. Basically. We could use abstract codes (for example. and W (for East. each column in each table must have a data type assigned to it. Humphrey Stadium. Column stadium is a 30−character column.

We could make this field a one−character array. a small integer will be more than adequate. CREATE INDEX index4 ON game (visiting_team). It has the following syntax:
CREATE INDEX [ UNIQUE ] index_name ON table_name ( column_name [ . CREATE INDEX index3 ON game (home_team). the names of the columns that comprise the index are enclosed in parentheses. no two rows can contain the same value for the column or columns for which you build the index. which means that it can hold a maximum value of 32. Most SQL packages have robust methods for comparing columns of different types. ] )
The keywords CREATE INDEX can optionally be followed by the keyword UNIQUE. we might wish to give column game_number type TIME (if our database package supported such a typesome do not) or combine it with column game_date in the form of a TIMESTAMP data type (again. that would make this field unlike the other fields in this database that hold numeric information. As you can see.
As you can see.foreign key. as in this instance. even if it does waste a byte occasionally. yet not so many that they hog your systems resources. game_number). for obvious reasons. however. CREATE UNIQUE INDEX index2 ON game (home_team. it must have the same data type as the column it is referencing. we will go into database design in much greater detail. Its a judgment call. a SMALLINT is two signed bytes. Column game_date is a DATE.767which should be enough for any baseball game. CREATE INDEX: Create an index The tables that comprise our baseball database are created. and the next step is to build some indexes for these tables. As we noted in Chapter 2. This keyword tells SQL that you want this index to be uniquethat is. 70
. but we believe it is best to put all numeric information into a numeric type. game_date. Column game_number is of type SMALLINT. if our database package supported such a type). This column holds the number of a game played between two teams on a given date. Because building an index consumes system resourcesboth disk resources and CPU cyclesa key part of designing a database is devising the right combination of indexes: enough indexes so that your commonly executed queries are smooth and fast. The script in Listing 3−4 creates the indices for our baseball database: Listing 3−4: Creating Indices
CREATE UNIQUE INDEX index1 ON team (team_name). The following subsections build indices for our example database. so that we can distinguish the two games of a double−header. and discuss these issues more explicitly. you must keep any number of considerations in mind when you design even a trivial database. If we had decided in Chapter 2 to record the games number as the time the game started. but you are simply creating trouble for yourself and for your program if you assign to a foreign key a data type other than that of the column it is referencing. Columns home_team_runs and visiting_team_runs are both assigned type SMALLINT. This kind of index gives you a rough−and−ready sort of primary keywith the exception that it cannot be referenced by a FOREIGN KEY clause in another table. As this column will always hold 1 or 2. In Chapter 4. an index helps to speed the searching of data on an index. Under most implementations. The SQL statement CREATE INDEX creates an index.

to drop index index1 under MySQL. if you want more information. you would use the following SQL statement:
DROP TABLE bad_table. MySQL uses its own nonstandard version of the ALTER TABLE instruction to drop an index. but not both.
MySQL does not support this statement. it enables you to remove. and its implementation varies quite a bit from one database package to another. ALTER TABLE is rather advanced. RESTRICT tells the engine not to drop the table if it discovers that any other table references table_name through a foreign key. change the type of a column.
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. you would execute the following SQL statement:
DROP INDEX index1. In our syntax diagrams. as its name implies. DROP TABLE The statement DROP TABLE drops a table from your database. likewise. For example. see the documentation that comes with your database package. as you can probably guess. the vertical−bar character | means exclusive or: in this instance. and all indexes that had been built on that table. lets you alter the structure of a table. you would use the SQL statement:
ALTER TABLE team DROP INDEX index1. It has the following syntax:
DROP TABLE table_name [ CASCADE | RESTRICT ]
The keywords DROP TABLE are followed by the name of the table you wish to drop.The keyword UNIQUE indicates that the index must not allow duplicate values for this column or combination of columns. Instead. The name of the table can optionally be followed by the keyword CASCADE or the keyword RESTRICT. you also throw away all data that the table contains. Thus.
Naturally.
The instruction ALTER TABLE. or drop. drops an index. You can add columns to a table. CASCADE tells the engine to cascade through the database and remove every table that has a foreign key that references the table being dropped. It has the following syntax:
DROP INDEX index_name
To drop index index1 from database example. tables and indices from a database. when you drop a table. or (in some implementations) delete columns from a tablewhile preserving the data that are already loaded into the table. to drop the table bad_table from the database example. DROP INDEX The statement DROP INDEX. you can use either the keyword CASCADE or the keyword RESTRICT.
DROP: Remove a table or index
SQL enables you to add tables and indices to your database.

Its syntax takes several forms. Fulton County Stadium. we declared that none of its columns could contain NULL. If you do so. We describe each in turn. When an INSERT statement does not include a column_name clause. As we noted earlier. names the columns in the order in which we declared them in the CREATE TABLE statement with which we created table team. for example. All columns that you do not name in this clause will have NULL inserted into them. INSERT INTO team (city. which inserts a record for the Chicago Cubs. division. league) VALUES (Atlanta. The VALUES clause gives the values that you are inserting into table table_name. the INSERT statement does not care what order the columns appear in. A. Inserting literal values The first form of the INSERT statement enables you to insert values directly into a table:
INSERT INTO table_name [ ( column_name [. as long as the values given in the VALUE clause appear in the same order as do the columns named in the column_name clause.
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. N). inserts data into a table. We must do this because when we defined team. league. E. The second INSERT statement changes the order of the columns. The data type of each value must match that of the column into which it is being inserted. C). The first two INSERT statements name the columns explicitly. city. with the values being a set of literal values that you name. the following script inserts three records into table team of our baseball database:
INSERT INTO team (team_name. As you can see. if a column in table table_name accepts NULL. C). SQL assumes that the VALUE clause will contain a value for each column in table table_name. does not use a column_name clause. INSERT INTO team VALUES (White Sox. If you do not use this clause. There must be one value for each column that is named in the column_name clause.
Each of the three INSERT statements inserts a value into each of the five columns in table team. stadium. you cannot insert a text string into a column with the data type of INTEGER. Braves. N. Wrigley Field. Chicago. team_name. there must be one value for each column in the table. the default is to insert a value into every column of the table. SQL will insert NULL into that column.INSERT: Insert a row into a table
The SQL statement INSERT. Variable table_name names the table into which the values will be inserted. The third INSERT statement. division) VALUES (Cubs. For example. and that the values will appear in the same order as did the columns in CREATE TABLE statement with which you created table table_name. which inserts a record for the Chicago White Sox. Comiskey Park. ] ) ] VALUES ( value [. stadium. you can exclude it from the column_name clause. Character data must be enclosed in quotation marks. if the statement does not have a column_name clause. The optional column_name clause names the columns within table table_name into which you will be inserting values. ] )
This form enables you to insert one row into a table. Chicago. The first. as its name implies.

The columns that the SELECT statement returns must correspond with the columns in table table_name. respectively. Under MySQL. then the statement will continue to work even if you use the ALTER TABLE instruction to change the schema of the table. If this clause is not included. the SELECT statement must not return NULL for that column. Transfer values from other tables The second form of the INSERT statement transfers values from one or more tables into another. The FIELDS TERMINATED BY and LINES TERMINATED BY clauses give. If you do so. the selected data are bundled into rows that the statement returns. and that the fields come in the same order as do the columns in table table_name (as set by the CREATE TABLE statement that initially created the table). the optional column_name clause names the columns into which data will be loaded. Finally. (The SELECT statement. most SQL packages include a third form that enables you to insert data into a table from a file. We give some examples of the INSERT statement when we discuss the SELECT statement. The script in Listing 3−5. The syntax for this form of the INSERT statement is specific to the SQL package you are using. this form of the INSERT statement has this syntax:
LOAD DATA INFILE file_name INTO TABLE table_name FIELDS TERMINATED BY term_char LINES TERMINATED BY term_char ( column_name [.) The rows that the SELECT statement returns are inserted into table table_name. then MySQL assumes that each row in file file_name holds exactly one field for each column in table table_name. ] )
file_name names the file that holds the data to be loaded. If a column cannot accept a NULL value. the character that terminates a column (field) within a row and the character that terminates the line (row). Do a mass insertion The SQL standards describe only the two forms of the INSERT statement given above. table_name names the table into which the data will be loaded. However. Each row in the file must hold exactly one record to be inserted into the table in question. as you may suspect. both in data type and in domain.As a note of caution. It has the following syntax:
INSERT INTO table_name [ (column_name [. We describe it later. selects data from tables. loads data into the tables in our baseball database: Listing 3−5: Loading Data 73
. we believe it is worthwhile always to name the fields explicitly within an INSERT statement. later. ] ) ] SELECT select_statement
This form of the INSERT statement replaces the VALUES clause with a SELECT statement.

Camden Yards. SQLs SELECT statement is based upon relational calculus: it is descriptive rather than prescriptive.
SQL and relational calculus
In Chapter 2. Everything else in this bookfrom the relational theory that preceded this chapter. the SELECT statement can be extraordinarily complex. in how they describe the relation to be built. home_team_runs.Comiskey Park. without prescribing in detail how that relation is to be built. including SQL. to database administrationare all aimed toward this one simple. relational calculus is descriptive: it enables you to name one or more existing relations. The SQL statement SELECT selects data from the database.Baltimore. In our opinion.
Selecting Data from the Database
To this point. action of selecting data from the database.Chicago.LOAD DATA LOCAL INFILE bb_team.Anaheim Stadium. These mathematical systems serve as the bases for all languages with which we interrogate relational databases. LINES TERMINATED BY \n (home_team.data INTO TABLE team FIELDS TERMINATED BY .E Angels.A. Relational algebra is prescriptive: it defines discrete actions with which you can modify one or more existing relations in order to build a new relation.W
Please note that when you load data from a file.
The following gives a few rows from file bb_team.
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. LOAD DATA LOCAL INFILE bb_game. and how to load data into it.A. the SELECT statement is the heart of the relational database. However.Boston. Both the relational calculus and the relational algebra modify existing relations in order to build a new relation. LINES TERMINATED BY \n (team_name. stadium. league. it also contains features drawn from relational algebra. to help you deal with knotty problems. and then to describe the relation that you want built from it. However. division).data INTO TABLE game FIELDS TERMINATED BY . Baseball fans may note that the information here is obsolete.E Red Sox.Fenway Park. we have discussed how to build a database. game_date. so you can see how data must be laid out in a file for mass loading. that is because we are using information from the year 1992:
Orioles.Anaheim. The next step is to retrieve data from the database. to the C and Java programming. if you can master the SELECT statement. city. we discussed relational algebra and relational calculus. you do not have to enclose character data between quotation marks.A. yet vital.data. They differ. As you will see. game_number).A. through database design. This is a major difference from the INSERT statement. however.W White Sox. visiting_team_runs. visiting_team. you will have mastered the one most important feature of SQLand of the relational model. On the other hand.

you can try something slightly more complex. the SELECT statement in its simplest form has this syntax:
SELECT column_name FROM table_name
column_name names a column within the database.
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. we will lead you gradually to an understanding of this most useful of statements. the script in Listing 3−6. FROM table_name ]
For example. Each step of the way. selects the contents of column team_name from table team in database baseball: Listing 3−6: Selecting a Team Name
SELECT team_name FROM team. we show the syntax of the SELECT statement. For example. with a portion added to reflect the complication that we are discussing at the moment. and gradually work our way to its more complex forms. this returns the following data:
team_name Orioles Red Sox Angels White Sox
Selecting multiple columns
Now that youve seen the SELECT statement in its simplest form. The syntax to do that is:
SELECT column_name [ .
When executed under MySQL. the script in Listing 3−7 selects the name of the team and its league from our baseball database: Listing 3−7: Selecting Team Name and League
SELECT team_name. The column clause To begin. We begin with its simplest form. In this way. league FROM team. You can use the SELECT statement to select multiple columns from within your database.One−table selection
This section describes the SELECT statement gradually. table_name names the table within which that column resides.

and the type of each column. league) SELECT team_name. so. which selects attributes from a relation. when we discussed relational algebra. This is a very important point: Just as each operation in the relational algebra and the relational calculus creates a new relation as its product. The rows are defined in the WHERE clause. this statement prints the following on your screen:
team_name league Orioles A Red Sox A Angels A White Sox A
In Chapter 2. Rather.
The INSERT statement funnels the output of the SELECT statement into the newly created table temp_team.
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.
Building a new table
You may have noticed that the output of the SELECT statement is in the form of rows and columns: one column for each column named in the column_name clause of the statement. The above form of the SELECT statement simply implements the relational project operation. a solitary asterisk * in the column_name clause is a synonym for all columns in the table or tables named in the FROM clause. too. Please note that the number of columns within the SELECT statement. and one row for each row in the table from which we are selecting data. This new table is not added to your database. DROP TABLE temp_team.When executed under MySQL. the SQL engine will complain. league CHAR(1) NOT NULL ). league FROM team. One note: Under most implementations of SQL. must match those of the table into which its output is being funneled. The columns of this new table are defined by the column_name and FROM clauses of the table. the SELECT statement creates as its product a new table. As we noted earlier. otherwise. you can embed a SELECT statement within an INSERT statement to populate a table within your database. the program:
SELECT * FROM game
selects every column from table game. The script in Listing 3−8 adds a new table to the baseball database and uses a SELECT statement to populate it: Listing 3−8: Adding a New Table
CREATE TABLE temp_team ( team_name CHAR(15) NOT NULL. For example. INSERT INTO temp_team (team_name. we described an operation called project. it is returned to whatever program used the SELECT to select data from the database. which are described in detail later.

and the number of runs scored by the home team is doubled.
The asterisk * here is the multiplication operator. when we introduce the WHERE clause to the SELECT statement. enables you to build a filter with which you can define the rows that you want to select from the table. FROM table_name ]
The bar character | here means orthat is. home_team_runs. or an arithmetic expression. you can also use constants and arithmetic expressions as data items within the column_name clause of a SELECT statement.
The restrictive WHERE clause
So far. it appears as follows:
SELECT column_name | constant | expression [ . If you wish. The output begins as follows:
home_team Blue Jays Indians Brewers Tigers Twins Yankees home_team_runs 5 1 2 4 5 0 this this this this this this this is is is is is is is a a a a a a a constant constant constant constant constant constant constant home_team_runs * 2 10 2 4 8 10 0
The constant this is a constant is embedded in each row of the table that the SELECT statement returns to the screen. thus.Constants and expressions
The SELECT statement can do more than just retrieve data items that already reside within the database. a given item named within the column_name clause must be a column name. selects rows from table game. we have used the SELECT statement to select individual columns from a table. home_team_runs * 2 FROM game. Each of our examples has selected every row from a table. and a third an arithmetic expression. This example. the following example gives you a taste of how they would be used in the column_name clause. The column_name clause can mix items of different types: one item can be a constant. and adds a constant: Listing 3−9: Select
SELECT home_team. however. When we add this feature to the syntax of the SELECT statement. We discuss both constants and arithmetic expressions later. this is a constant. The SELECT statement. the phrase home_team_runs*2 multiplies the value of column home_team_runs by 2. or a constant. The following section discusses constants at greater length. doubles the number of runs scored by the home team. Listing 3−9. However.
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. a second can be a column name.

Constants come in four different flavors: numeric. You must prefix a negative numeric constant with a −. and what constants can be compared with which columns: 78
. as its name implies. an expression appears most often in the WHERE clause of an INSERT. For example. That being said. but you do not have to do so. much of the power of SQL resides in its ability to understand subtle and complex restrictive expressions. is a number. However. Such a constant can be either an integer constant or a floating−point constant. we must first introduce two of the elements that comprise an expression: constants and operators. FROM table_name [ WHERE restrict_expression ] ]
The rest of this section describes the restrict_expression. including this new clause:
SELECT column_name | constant | expression [ .333E97
SQL implements some rules about how it performs arithmetic upon constants.
Numeric constants
A numeric constant.15E−8 −33. It contains a decimal point and it may also contain an E to indicate an exponent. and symbolic. the following are floating−point constants:
1. or the data in a column.0 3. string. that implements the restrict operation. Constants SQL. a little time spent with this section will pay big dividends in terms of your ability to use relational databases well. lets you use constants within an expression. therefore. A SQL program can use an expression to calculate a value that the program uses to control the selection of data from the database. and checks whether the row meets the criteria that you set. if the row meets those criteria. called the WHERE clause. For example. This operation examines an individual row (or. lets begin with some definitions. We must warn you that what follows introduces several concepts.You may remember from our discussion of relational algebra in Chapter 2 that relational algebra includes an operation called restrict. as its name implies. to use the technical term tuple) within a relation. An expression is a phrase of code that uses an operator to modify either a constant. the following are all integer constants:
1 +15 36793561879035160 −273
Note that a numeric constant does not contain commas. it inserts that row into the relation it is building. The following gives the syntax of the SELECT statement. You may prefix a positive number constant with a +. DELETE. The SELECT includes a clause. date/time. An integer constant is. an integer. Before we show how expressions are used within a WHERE clause. or SELECT statement. like most other languages. no matter how long it is. or the product of another expression.1416 97. Thus. A floating−point constant encodes a floating−point number.

The 1992 ANSI/ISO standard for SQL requires that a string constant be enclosed between apostrophes (aka single−quotation marks).
String constants
A string constant is. Please note that database packages differ with regard to how they handle case when they compare data with string constants. such as MySQL. for example. INTEGER or SMALLINT. the SELECT statement
SELECT * FROM team WHERE name = CUBS
will not return anything when run under Sybase. if youre checking whether column birthdate is set to August 27. that is. In this instance. the result is of type FLOAT. and the format DD/MM/YYYY for dates in Europe. such as Sybase. do not by default take case into account when they compare strings. You can compare these constants with the contents of columns that have a date data type or a time data type. 1952. For example. If you are not sure whether your database package does so. do take case into account. For example:
This is an apostrophe within a string constant
Most database packages also let you enclose string constants between quotation marks (aka double−quotation marks). the format of a date or time string varies. for example.
Date and time constants
A date and time constant is a string that describes a date or a time. they let you compare an integer constant with a floating−point column. However. there is no need to escape apostrophes. Some database packages lift these restrictions. Some packages. the result is of type FLOAT. A literal apostrophe within a string constant must be escaped by inserting an extra apostrophe before it. the result has type INTEGER. you should not assume that a database package does lift this restriction until you check its documentation. but it will return the row for the Cubs when run under MySQL. Most database packages recognize the format MM/DD/YYYY for dates in the United States. Unfortunately. • You can compare a floating−point constant (or the product of performing arithmetic upon a floating−point constant and another numeric constant) only with a column that has a floating−point data type. depending upon your locale and the database package you are using. • If you perform arithmetic upon two floating−point constants. For example:
"This is an apostrophe within a string constant"
Again. FLOAT or DOUBLE. • You can compare an integer constant (or the result of performing arithmetic upon two integer constants) only with a column that has an integer data type. or vice versa. use the expression
birthdate = 08/27/1952
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. For example. whereas other packages.• If you perform arithmetic upon two integer constants. as its name implies. • If you perform arithmetic upon a floating−point constant and an integer constant. a string. check its documentation. not every database package recognizes string constants that are enclosed between quotation marks.

Before you use a symbolic constant in any of your SQL programs. and operators that perform comparisons. DB2 represents todays date as the constant CURRENT DATE.
Symbolic constants
Finally.
Arithmetic operators
SQL recognizes these arithmetic operators: + Addition − Subtraction * Multiplication / Division The above operators are recognized by every implementation of SQL. not on strings. or Aug 27. dates. a symbolic constant can name the person who is using the system now. Unfortunately. FALSE. or todays date. Symbolic constants are very useful. For example. or NULL). Some implementations of SQL recognize their own proprietary operators. Operators An operator is the verb of an expression: it tells the expression what to do. 1952.
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. whereas a comparison operator yields a logical result (either TRUE. others do not. symbolic constants also vary wildly from one database package to another. Some SQL packages recognize constants of the form August 27. 1952. We first discuss the arithmetic operators.in the United States. SQL includes operators that perform arithmetic. Check the documentation that comes with your database package to see what constants it does and does not recognize. and then we discuss the wide range of comparison operators. such as the following: % Modulus || Concatenate strings Arithmetic operators can be used only on numeric data types. be sure to check the documentation that comes with your package. For example. A symbolic constant represents some value that is constant to the system as it is being used right now. most database packages implement symbolic constants. An arithmetic operator yields a number as its output. and the expression
birthdate = 27/08/1952
in Europe. or any other nonnumeric type. whereas Oracle represents it as the constant SYSDATE and Informix as the constant TODAY. but these differences among packages make symbolic constants very difficult to use in a portable manner.

If home_team_runs equals a number other than 5.
BETWEEN
The operator BETWEEN. If title equals a string other than Linux Database. then this expression evaluates to TRUE. here you see it in action. as its name implies. If. the following checks whether the value of column title equals the title of this book:
title = Linux Database Bible
If title does equal Linux Database Bible. For example. then this expression evaluates to FALSE. For more information on how text is ordered and compared. be sure to check the documentation that comes with your database package. whether one string comes earlier in the alphabet than the other. among other things. Also. gives you an easy way to check whether a column lies within a range of values. strings that contain punctuation marks and digits may not compare as you think they should. TRUE. For example. home_team_runs is not set to any number at allif it is NULL. then this expression evaluates to FALSE. then this expression evaluates to TRUE. Its syntax is:
column BETWEEN element AND element
For example. Each expression that is built around a comparison operator returns a logical value as its resultthat is. FALSE. in other wordsthen this expression evaluates to NULL. the following compares the value of the numeric column home_team_runs with the numeric constant 5:
home_team_runs = 5
If home_team_runs equals 5. we discussed the relational models three−tiered logic. the following operators let you compare SQL expressions: = Equal <> Not equal < Less than <= Less than or equal > Greater than >= Greater than or equal Most packages also recognize the operator != for not equal. This means. Please note that most database packages use ASCII values when comparing text. then capital letters will be regarded as coming earlier lexically than do lower−case letters. however. or NULL. If. that if a database package takes the case of text into account. when used between two strings. although this is an extension to the SQL92 standard. The equality operator =. however. indicates whether the strings are identical. you can use the following expression to determine whether its value lies between 1 and 10. you may have the odd result of a string that begins with Z has a lower lexical value than a string that begins with a. title is NULL. inclusive: 81
. In Chapter 2. if home_team_runs is a numeric column.Comparison operators
To begin. SQL lets you use the comparison operators to compare strings as well as numbers. thus. then the expression evaluates to NULL. The inequality operators also indicate whether one string is lexically greater than or less than the otherthat is. We provide further examples of these operators in action later.

home_team_runs BETWEEN 1 AND 10
This is equivalent to saying:
home_team_runs >= 1 AND home_team_runs <= 10
You can use BETWEEN to check whether a string lies between a given lexical range. it is unusual to use an expression in this operation. it is difficult to predict just what the outcome will be. 3. Please note that an element used in a BETWEEN operation is usually a constant. the % represents an indefinite amount of text of any kind. However. We will give an example of this below. and partly because they are inconsistently implemented across database packages. For example. because if an element logically evaluates to NULL. George. when we introduce the operator LIKE. this is more trouble than it is worth. This is partly due to ANSI/ISO SQLs rules governing how BETWEEN handles NULL expressions being quite convoluted. Under SQL. Ivan. but it can be an expression.
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. the following expression checks whether column first_name has any of five values:
first_name IN (Marian. Thus. the following expression checks whether a given teams name begins with any of the first five letters of the alphabet:
name BETWEEN A% AND E%
Note the use of the % as a wildcard character. Usually. )
Every element in the list must match the type of columneither numeric. For example. text. element. Richard)
An element in the list can itself be an expression. You can also use BETWEEN to check whether a date lies between two other dates. the following checks whether the value of column home_team_runs equals any of three given values:
home_team_runs IN (1. Catherine. However. the following checks whether the value of column birthdate lies in the first six months of 1952:
birthdate BETWEEN 01/01/1952 AND 06/30/1952
The date constants must conform to those recognized by the database package. when we discuss sub−SELECTs. 5)
This is equivalent to the expression:
home_team_runs = 1 OR home_team_runs = 3 OR home_team_runs = 5
Again. We discuss wildcards at greater length later.
IN
The operator IN checks whether the value of a column matches any value in a list. For example. It has the following syntax:
column IN ( element. or date. A% represents any string that begins with a capital A. there is one exception to this rule: sometimes you may wish to use another SELECT statement to build the list of values used by the IN clause.

Note that the first and last instances of % are unescaped. how would you match a string that contains a literal % or a _ within it? In most instances. SQL2 describes a clause called ESCAPE. The above expression matches all of the following titles:
Linux Database Bible The Linux Data Base Bible Linux Databases Forever Linux The Worlds Greatest Linux Releases The Great Big Book of Linux Programming Tips Linux
If you wanted to match the string something Linux something.LIKE
The operator LIKE is used only with strings. One problem arises: How do you escape the wildcard charactersthat is. then this expression evaluates to TRUE. then % is equivalent to the shells wildcard character *. it does not match zero charactersso the above expression forces LIKE to match only the book titles that have at least one character to the left of Linux and at least one character to the right. the expression uses the ESCAPE clause to declare that the character @ is the escape character. and expect LIKE to treat it as a constant.
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. including an _. and _ is equivalent to the shells wildcard character ?. to see whether column title holds the string something %%Linux%% something. and so remain wildcard characters. What you cannot do is embed an % or an _ within a string. For example. For example. and _ matches any single character. and then uses the @ to escape the wildcard character %. It has the following syntax:
column LIKE pattern
pattern combines string constants with wildcard characters. The % character matches any range of characters. and if it does not contain a title. you could use the following expression:
title LIKE % @%@%Linux@%@% % ESCAPE @
In this example. then this expression evaluates to NULL. you would use the following expression:
title LIKE %_% Linux %_%
The wildcard character _ matches any one characterunlike %. if it contains a title that does not contain the string Linux. this is not a problem. prefixing the wildcard with the escape character tells LIKE to treat the wildcard as a literal character. with which you can define a character that escapes a wildcard characterthat is. including % itself. the following expression checks whether the column title contains the string Linux:
title LIKE %Linux%
If title is set to a title that contains the string Linux. SQL recognizes two wildcard characters: % Match zero or more characters _ Match any one character If you are familiar with the UNIX shell. then this expression evaluates to FALSE. It checks whether a string matches a given pattern of strings.

It is guaranteed always to evaluate to TRUE or FALSEnever to NULL.
IS
We must consider one last operator: the IS operator. column ssn is not NULL. however. However. it is a problem if the expressions
FOO = NULL
and
FOO <> NULL
both evaluate to NULL rather than to TRUE or FALSEneither tells you whether FOO is NULL or not. use the expression:
ssn IS NOT NULL
The IS operator could. it is a flag that indicates the absence of a value. to determine whether. so good. in theory. but this does raise a problem: How can you write an expression to tell whether something is NULL? After all. column ssn is NULL. when we discussed the relational model. A simple expression is one whose operands consist only of columns or constants. you cannot use LIKE to match exactly a string that contains % or _. you can stack expressions within eachor nest the expressions. it makes sense simply to examine whether the column is NULL. a constant. SQL introduces a special operator: IS. an expression in a SQL WHERE clause evaluates whether the contents of a given column within your database match a criterion that you set. this result governs whether a given SQL statement is executed for a given row within your database. then the expression is said to be complex. in a given row. This operator examines whether a variable is or is not NULL. a comparison operation returns NULL only if one of the columns being compared is itself NULL. IS is not exactly a comparison operator. it checks whether a given column is set to NULL. or NULL. in turn. An operand can be a column (or to be more exact. The unfortunate fact is that for all practical purposes. NULL is not a value. rather than to examine the result of an expression that includes the column. Every expression is built around an operatorthe verb of the expression. 84
. it yields a logical valueTRUE. that missing data are indicated with NULL. Thus. rather. You may recall from Chapter 2. For example. FALSE. Because an operand can be another expression. in a given row. An operator. operates upon one or more operands. As we show later.The problem with this approachapart from the fact that it is extremely clumsyis that many implementations of SQL do not recognize it. So far. to determine whether. if one or more of the expressions operands is another expression. the data in a column). or the output of another expression. Any comparison with NULL returns NULLeven when you compare NULL with NULL. rather. To get around this problem. use the expression:
ssn IS NULL
Likewise. be used to check whether the logical result of a comparison operation was NULL. when an expression is used in a WHERE clause. Thus. Assembling an expression As we noted at the beginning of this section.

home_team_runs FROM game WHERE home_team_runs <= 5. demonstrates this: Listing 3−10: Comparison With a Constant
SELECT home_team.Thus. in other wordsthen this expression returns NULL. this expression returns TRUE. or Brewers: 85
. Or. For example. however. the following expression checks whether home_team_runs in the row now being examined holds a value that is greater than that held by visiting_team_runs:
home_team_runs > visiting_team_runs
The script in Listing 3−11 demonstrates this: Listing 3−11: Comparing Two Columns
SELECT home_team. If the value to which home_team_runs is less than the value to which visiting_team_runs is set. A simple expression compares two columns. In addition to comparing a columns value with a constant.
Simple expressions
Now that we have introduced what an expression is. game_date FROM game WHERE home_team_runs > visiting_team_runs. home_team_runs is set to no value at allif it is NULL. this expression returns FALSE. if column home_team_runs holds a numeric value. an expression can compare the values of two columns. you can build very elaborate tests for the contents of one or more columns within your databasea complex expression can be complex indeed. however. although SQL offers only a handful of operators and constants. in other wordsthen this expression returns NULL.
If column home_team_runs for a row contains a value that is less than or equal to 5. For example. then this expression returns TRUE. which is set to a string data type. we begin to circle back and show how expressions are used within a WHERE clause.
If the value to which home_team_runs is greater than the value to which visiting_team_runs is set. then this expression returns FALSE. If. or compares a column with one or more constants. White Sox. the following checks whether its value is less than or equal to 5:
home_team_runs <= 5
The script in Listing 3−10. If home_team_runs within that row is set to a value that is greater than 5. If. We can see if FIRSTNAME is set to the value Yankees. either home_team_runs or visiting_team_runs has no value at allis NULL. consider the column home_team.

At the risk of being repetitive. If it is set to any other string. For a slightly more complicated example. the subexpression involves an arithmetic operator. not just one of two as with most other computer languages. or NULL. that we wanted to find all games in which the home team scored at least twice as many runs as the visiting team.
Complex expressions
As we noted earlier.home_team IN (Yankees. White Sox. game_date FROM game WHERE home_team_runs > ( visiting_team_runs / 2 ). however. Brewers).
The parentheses indicate that you want the arithmetic operation performed before the comparison is performed. White Sox. we must emphasize that SQL expressions implement the relational models three−tiered logic: any expression can return TRUE. home_team is NULLif it has no value at allthen this expression returns NULL. FALSE. Brewers)
The script in Listing 3−12 demonstrates this: Listing 3−12: Comparison With a List of Constants
SELECT home_team. this expression returns TRUE. If. When you write an SQL expression. we must first divide visiting_team_runs by two. In the above example. this expression returns FALSE. this is not necessary. For example. consider again this expression:
home_team_runs > visiting_team_runs
Lets say. In most instances. This is another expression that checks whether the home team scored at least twice as many runs as the visiting team:
( visiting_team_runs * 2 ) <= home_team_runs
And another way is: 86
. you must be prepared for the fact that it can return one of three logical results. as follows:
home_team_runs > ( visiting_team_runs / 2 )
Listing 3−13 demonstrates this: Listing 3−13: A Simple Arithmetic Expression
SELECT home_team. game_date FROM game WHERE home_team IN (Yankees. consider the following complex expression. and then compare the result with home_team_runs. but the parentheses do make the expression easier to read. White Sox. however. a complex expression is one in which an operand is itself an expression. To determine this. or Brewers.
If home_team is set to Yankees.

As an example. so it is buggy. it has a bug: if the visiting team is shut out (that is. in turn. this expression does not correctly handle games in which the visiting team was shut out. however. Chapter 2 gives the truth tables for AND and OR operations. it scores no runs). and then our introduction to expressions is complete. they will exclude all rows in which visiting_team_runs is zero. Here. we were interested in whether the home team scored twice as many runs as the visiting team. In Listing 3−14.
This last example demonstrates how expressions can be nested within each other. Each returns a logical value. of course. then this expression may attempt to divide by zerowhich is. impossible. and the right operand of that subtraction expression is itself a multiplication expression.
AND and OR
One last subsection. You can use the logical operators AND and OR to couple expressions together.( home_team_runs − visiting_team_runs ) <= home_team_runs
Or again:
( home_team_runs − ( visiting_team_runs * 2 ) ) >= 0
Listing 3−14 demonstrates this last example: Listing 3−14: A More Complex Arithmetic Expression
SELECT home_team. If either home_team_runs or visiting_team_runs were NULL. Most SQL engines protect you against this problem: that is. then its expression (even an arithmetic expression) would also yield NULLafter all. would render the entire expression NULL. let us now change that to examine whether the winning teamhome or visitorsscored at least twice as many runs as the losers. game_date FROM game WHERE (home_team_runs − ( visiting_team_runs * 2 )) >= 0. rather than attempt to divide by zero and crash. Please note that the expression
( home_team_runs / visiting_team_runs ) >= 2
also appears to select the games in which the home team scored twice as many runs as the visiting team. However. Each of these logical operators takes two operands. depending upon the logical value of its operands. consider the baseball game we described above. multiplying or dividing NULL yields NULLand that. you may wish to review them quickly. the left operand of the >= expression is a − (subtraction) expression. However. The following complex expression discovers this:
( ( home_team_runs * 2 ) <= visiting_team_runs ) OR ( ( visiting_team_runs * 2 ) <= home_team_runs )
Listing 3−15 demonstrates this: 87
.

game_date FROM game WHERE home_team_runs IS NOT NULL AND visiting_team_runs IS NOT NULL AND (((home_team_runs * 2) <= visiting_team_runs) OR ((visiting_team_runs * 2) <= home_team_runs)) AND ((visiting_team_runs + home_team_runs) >= 6). game_date FROM game WHERE ((home_team_runs * 2) <= visiting_team_runs) OR ((visiting_team_runs * 2) <= home_team_runs). then the expression as a whole yields FALSE.
The above expression returns TRUE if the home team scored at least twice as many runs as the visiting team. both subexpressions will return FALSE. and in which more than six runs were scored. Of course. as columns home_team_runs and visiting_team_runs were created with the NOT NULL clause. and the overall expression therefore will also return FALSE. For example. If we wish to avoid having it return NULL. game_date FROM game WHERE (((home_team_runs * 2) <= visiting_team_runs) OR ((visiting_team_runs * 2) <= home_team_runs)) AND ((visiting_team_runs + home_team_runs) >= 6)
Note the use of parentheses to make clear just which operands are associated with which operators. we can explicitly check for NULL. In games in which the winner did not score twice as many runs as the loser. if either home_team_runs or visiting_team_runs is NULL. or vice versa. we should not have to do so. then the entire expression evaluates to NULL as well. then the expression as whole is NULL. This expression in the WHERE clause yields TRUE if the winning team scored twice as many runs as the loser. consider the example given immediately above. and so cannot contain NULL. Once again. particularly when a column can contain NULL. Strictly speaking.Listing 3−15: Comparison Using Keyword OR
SELECT home_team. The script in Listing 3−17 checks for NULL in either column: Listing 3−17: Checking for NULL
SELECT home_team. The script in Listing 3−16 is an example of how to do this: Listing 3−16: Comparison Combining Keywords AND and OR
SELECT home_team. if either home_team_runs or visiting_team_runs is NULL. you can use the operator IS to check for NULLity. however. this is a good "defensive programming" practice. As you recall. and both teams together scored at least six runs. Consider further that we are interested in every game in which the winning team scores twice as many runs as the losing team. One way to avoid having an expression return NULL is to check for NULL explicitly. If either of those conditions is false.
88
.

If either is NULL. however. Two−table join: An example The best way to grasp how a multiple−table join works is to see it in action. As you can see. then this AND expression is FALSE. With these additions. You will see many examples of restrictive WHERE clauses throughout the rest of this book. much of the power of the SELECT statement lies in the fact that you can use SELECT data from more than one than table.As you can see. we must add two elements to its syntax: • The FROM clause must name each of the tables whose data we are using. such. However. ] [ WHERE [ restrict_expression ] [ join_expression] ]
The join_expression indicates the joins between tables. ] FROM table_name [ . then the expression as a whole is FALSE. If either of the columns is NULL. Usually. The second AND expression
(((home_team_runs * 2) <= visiting_team_runs) OR ((visiting_team_runs * 2) <= home_team_runs)) AND ((visiting_team_runs + home_team_runs) >= 6). The first AND expression
(home_team_runs IS NOT NULL AND visiting_team_runs IS NOT NULL)
confirms that home_team_runs and visiting_team_runs is not NULL. The third AND cements the two together. In this way. • The WHERE clause must contain an expression that shows how the tables are joined. this gives the foreign keys that link the tables. it is rather a bother to check continually for NULLity in our expressions. We urge you to take a good look at them because mastering the restrictive WHERE clause is one of the most important steps toward mastering SQL. is the price SQL extracts for supporting NULL.
Multitable selections
Our discussion of the SELECT statement to this point has been limited to selecting data from a single table. this expression is built around three AND expressions.
performs our runs−scored computation. This concludes our introduction to expressionsand to restrictive WHERE clauses. the syntax of the SELECT statement now appears as follows:
SELECT column_name|constant|arithmetic_expression [ . To use more than one table in a SELECT statement. The script in Listing 3−18 prints out all games played in Comiskey Park:
89
. we ensure that our expression will always be TRUE or FALSE. or if the runs scored do not match our criteria.

home_team is the joinexpressionit shows how the tables team and game are joined.home_team. However. from the table built in step 3. 3. We included the name of the table in this clause to make it clearer. It uses the Cartesian−product operation to build a temporary table whose contents combine the contents of tables game and team. scored fewer runs) when playing teams in the American League East: Listing 3−19: White Sox Losses 90
. game_date FROM team. home_team. although we did not have to. It then uses the restrict operation to build a second temporary table from the table built in step 1. home_team. This newest temporary table consists of columns stadium. you may be asking yourself exactly what this statement is doing.Listing 3−18: Comiskey Park Games
SELECT stadium. This newer temporary table contains only the rows in which the value of column team_name equals that of column home_team. Two−table join: Another example Lets try another example of two−table joins. The final temporary tablethe one built using the project operationis the one that the SQL engine formats and displays on your screen. visiting_team_runs. The SQL engine then throws away all of the temporary tables that it built during this process. home_team_runs. in that order. as the names of the columns are not ambiguous. the SQL engine may not go through those steps literally. visiting_team_runs.
The output begins as follows:
Comiskey Comiskey Comiskey Comiskey Park Park Park Park White White White White Sox Sox Sox Sox Angels Angels Angels Angels 5 4 3 0 1 2 2 4 06−08−1992 06−09−1992 06−10−1992 06−11−1992
The clause team.team_name = game. At this point. visiting_team. Rather than literally building the four temporary tables described above.team_name = game. the engine will try to make best use of any indices that that you have built for the tables named in the FROM clause. and game_date. visiting_team. In particular. This new temporary table contains only the rows in which column stadium equals the string constant Comiskey Park. Finally. If you remember our discussion of relational algebra from Chapter 2. The script in Listing 3−19 selects every game that the White Sox lost at home (that is. We should point out that the above process describes what is happening logically within the SQL engine. 4. you can see that the above SELECT statement translates into the following algebraic actions with which it builds its output: 1. the SQL engine uses the project operation to build yet another temporary tablethis time. 2. the SQL engine uses some short cuts and optimizations to speed the processing of your SQL statement and to reduce the amount of memory used. game WHERE stadium = Comiskey Park AND team. It again uses the restrict operation to build a third a temporary table from the table built in step 2. home_team_runs.

The output begins as follows:
White White White White White White White Sox Sox Sox Sox Sox Sox Sox 2 0 0 2 2 1 2 Blue Jays 6 05−22−1992 A E Blue Jays 9 08−26−1992 A E Orioles 2 05−15−1992 A E Orioles 7 05−16−1992 A E Orioles 3 07−20−1992 A E Red Sox 2 07−04−1992 A E Yankees 4 08−15−1992 A E
Unions
As you may have guessed from the above examples. the baseball problem we stated just above. However imagine that we wished to find every game that the White Sox lost against Eastern Division teams. the other for the White Sox as the visitorsthen cement the results together.SELECT home_team. home_team_runs. Some thought will show that it is not possible to write a simple SELECT statement to execute this query. ] [ WHERE [ restrict_expression ] [ join_expression ] ] [ UNION SELECT select_statement ] ]
Consider. SQL gives us an elegant way to solve this problem: the UNION clause. The UNION clause lets us write two simple SELECT statementsone for the White Sox as the home team. The UNION clause cements together into one table the output of two or more SELECT statements. that you cannot debug it because you cannot readily understand just what it is supposed to do. This script selects every game that the White Sox lost at home against an Eastern Division opponent. simpler pieces. but basically it is a straightforward statement. the syntax for the SELECT statement appears as follows:
SELECT column_name | constant | arithmetic_expression [ .team_name AND division = E. With the addition of this clause. each of which you can debug individually. which SQL does not support. In fact.visiting_team = team. game_date. and this means. That is because we must somehow ensure that the White Soxwhether the home team or the visitorsscored fewer runs than their opponents. for example. and then cementing them together. The following SELECT statement implements this strategy: 91
. team WHERE home_team = White Sox AND home_team_runs < visiting_team_runs AND game. SELECT statements can become rather complex. as with writing any kind of computer program (or any kind of book). One key to writing SELECT statements. what can we do? Does this mean that SQL is not relationally completethat it cannot even execute simple. This script has some complexity to it. everyday questions? No. whether at home or on the road. division FROM game. it is quite possible to write a SELECT statement that is too complex to be readily understood. So. is to break the statement down into smaller. consider again the script in Listing 3−19. visiting_team_runs. league. In fact. For example. FROM table_name [. in turn. and there is no way to do that without using an "if" operator. This clause lets you tackle complex problems by writing a series of simple SELECT statements. visiting_team.

division FROM game.team_name AND division = E. visiting_team.home_team_runs. game. There is a work−around for UNIONa temporary table. team WHERE home_team = White Sox AND home_team_runs < visiting_team_runs AND game. home_team_runs. visiting_team_runs. The script in Listing 3−20 uses a temporary table to mimic a UNION: Listing 3−20: Mimicking a UNION
CREATE TABLE sox_lose ( home_team CHAR(15) NOT NULL. game_date.visiting_team. home_team_runs.visiting_team = team.team_name AND division = E
As the above example shows.visiting_team_runs. game. home_team_runs. game. game_date.SELECT home_team.home_team = team. league. game_date CHAR(10) NOT NULL. INSERT INTO sox_lose (home_team. team. division FROM game. including MySQL. team WHERE visiting_team = White Sox AND home_team_runs > visiting_team_runs AND game.game_date. game.team_name AND division = E UNION SELECT home_team. each SELECT statement that you join with the UNION clause must request exactly the same set of columns from your database.visiting_team = team. game.visiting_team. do not support UNIONs. visiting_team_runs. visiting_team_runs. game_date. league CHAR(1) NOT NULL.home_team. league.division FROM game.game_date. visiting_team_runs SMALLINT NOT NULL. home_team_runs.home_team_runs. team. some database packages. game_date.visiting_team_runs. visiting_team.
92
. all is not lost. team WHERE home_team = White Sox AND home_team_runs < visiting_team_runs AND game. team. visiting_team. league. However. visiting_team. game. game. division) SELECT game.league. division CHAR(1) NOT NULL ). In other words. league. division) SELECT game. home_team_runs SMALLINT NOT NULL. visiting_team_runs. visiting_team CHAR(15) NOT NULL. No UNIONs: A work−around Unfortunately. the column_name and FROM clauses of each of the SELECT statements must be exactly the same.home_team. INSERT INTO sox_lose (home_team.league. and in the same order. game.

SELECT * FROM sox_lose. team WHERE visiting_team = White Sox AND home_team_runs > visiting_team_runs AND game. When we add this clause to the syntax of the SELECT statement. the data that we have selected from our databases have appeared in no particular order. the DROP TABLE statement throws away sox_lose when we are done with it.home_team = team. However. it appears as follows:
SELECT column_name | constant | arithmetic_expression [ .
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. the script appears to be complex. The ORDER BY clause to the SELECT statement sorts the output of the SELECT statement. we give the columns the same names as those of the columns being selected. and you can sort by either ascending or descending order. You can sort by more than one column.division FROM game.team. league FROM team. It is embedded within an INSERT statement.team_name AND division = E. ] [ ASC|DESC ] ] [ UNION SELECT select_statement ]
The script in Listing 3−21 selects team names from the baseball database without sorting: Listing 3−21: Unsorted Teams
SELECT team_name. For the sake of convenience. It is embedded within an INSERT statement that writes its data statement into the new table sox_lose. DROP TABLE sox_lose. In this way. The use of temporary tables gives you a way to work around the absence of support for the UNION clause. • The third SELECT statement reads the contents of sox_lose and writes them to the screen. discrete SELECT statements that you can debug and run separately. which writes the output of the SELECT statement into the new table sox_lose. you can break seemingly intractable selections into a set of small. • Finally. but its really quite straightforward: • The CREATE TABLE statement creates a table called sox_lose. ] [ WHERE [ restrict_expression ] [ join_expression ] ] [ ORDER BY column_name [ ASC|DESC ] [. ] FROM table_name [. • The second SELECT statement selects the games in which the White Sox are the visitors. the SELECT statement includes a clause with which you can sort the output of a selection. as we do not want it cluttering up the database now that we have no more use for it.
At first glance. This table has the same number and type of the columns that we are selecting with our two SELECT statements. • The first SELECT statement selects the games in which the White Sox are the home team.
ORDER BY: Sort output
In our examples so far.

By default. Listing 3−24 replicates Listing 3−23.
The output of this script is as follows:
Angels Angels Angels Angels Angels Angels Angels Athletics Athletics Athletics Athletics Athletics Athletics Blue Jays
As you can see. sorts the output into alphabetical order: Listing 3−22: Alphabetical Sorting
SELECT team_name. from earlier dates to later. this means sorting by lexical (alphabetical) order. visiting_team. You can. Listing 3−23 demonstrates this: Listing 3−23: Sorting by Multiple Columns
SELECT home_team. visiting_team FROM game ORDER BY home_team. except that the output is written in descending order: Listing 3−24: Sorting in Descending Order 94
. however. home_team). visiting_team).
It gives the following output:
Angels Astros Athletics Blue Jays A N A A
You can also sort by more than one column.This script gives the following output:
Orioles A Reds A Angels A White Sox A
The next script. for number types. by numeric value. league FROM team ORDER BY team_name. the ORDER BY clause sorts data by ascending order. the ORDER BY clause first sorted the entire output by the first column you named (in this case. For example. Listing 3−22. which reverses each of these criteria. and for date types. specify descending order. For string types. then for each value of the first column sorted by the value of the second column you named (in this case.

Its output is:
Yankees Yankees Yankees Yankees Yankees Yankees Yankees Angels Angels Angels Angels Angels Angels Athletics
As you can see. home_team_runs. The modified SELECT statement would read as follows: Listing 3−26: UNIONs and ORDER BY
SELECT home_team. ORDER BY and UNIONs SQL restricts how you can sort the data generated by a SELECT statement that contains a UNION clause. team WHERE home_team = White Sox
95
. only the last SELECT clause within the SELECT statement can have an ORDER BY clause. the script in Listing 3−26 sorts the output of the example SELECT statement with which we demonstrated the UNION clause. In brief. you may ask why such a keyword is needed.SELECT home_team. division FROM game. visiting_team_runs. The script in Listing 3−25 demonstrates this: Listing 3−25: Mixed Sorting
SELECT home_team. For example. visiting_team FROM game ORDER BY home_team DESC. visiting_team DESC. whereas the names of the visitors are in ascending order. Now. league. the names of the home teams are in descending order. given that ascending order is the default? The reason is that you can mix your sorting: you can specify that some columns be sorted into ascending order and others into descending. visiting_team FROM game ORDER BY home_team DESC.
Its output is:
Yankees Yankees Yankees Yankees Yankees Yankees Yankees White White White White White White Twins Sox Sox Sox Sox Sox Sox
The keyword ASC tells the ORDER BY clause to sort into ascending order. This ORDER BY clause then affects the entire SELECT statement. visiting_team. visiting_team ASC. game_date.

visiting_team. The keyword ALL tells the SQL engine to retain them.team_name AND division = E UNION SELECT home_team. home_team_runs. visiting_team.visiting_team = team. consider Listing 3−27. it appears as follows:
SELECT [ DISTINCT|ALL ] column_name | constant | arithmetic_expression [ .AND home_team_runs < visiting_team_runs AND game. Rather. game_date. given that it makes no sense to sort the output of a SELECT clause before you mix it with the output of other SELECT clauses. it returns one pair of team names for each game played. ] [ ASC|DESC ] ] [ UNION SELECT select_statement ]
For example. In many situations. division FROM game. often you will want just one copy of every unique row that your SELECT statement generates. ] FROM table_name [. team WHERE visiting_team = White Sox AND home_team_runs > visiting_team_runs AND game. When we add this keyword to our syntax for the SELECT statement. which adds the keyword DISTINCT to the SELECT statement:
96
.home_team = team. which selects the names of teams from table game. returns the following:
Angels Angels Angels Angels Angels Angels Angels Athletics Athletics Athletics Athletics Athletics Athletics Blue Jays
that is. Listing 3−23. The keyword DISTINCT tells the SQL engine to throw away duplicate rows.team_name AND division = E ORDER BY home_team. For example. however. ] [ WHERE [ restrict_expression ] [ join_expression ] ] [ ORDER BY column_name [. league. visiting_team_runs.
DISTINCT and ALL: Eliminate or request duplicate rows
You may have noticed that most of the previous examples returned multiple iterations of a given row.
This restriction makes sense. The keywords DISTINCT and ALL enable you to control whether a SELECT statement outputs every row or only one copy of each unique row. you will not want to build a table that consists of multiple iterations of the same row. game_date.

As it happens. because many of the most important questions you will ask of a database will concern data that is missing: knowing that something did not occur can be as important as knowing that 97
. the SELECT statement begins its work by building a Cartesian product of the tables that are named in the FROM clause of the SELECT statement. visiting_team FROM game ORDER BY home_team. because the default for a UNION is to throw away duplicate rows. Please note that some database enginesin particular.
It generates the following:
Angels Athletics Angels Athletics
But wait a second. However. team_name FROM game. duplicate rows have been eliminated: the script printed only one copy of each unique row that the SELECT statement generated. because the SELECT statements default behavior is to retain duplicate copies of rows. What happened to the National League teams? The National League teams are missing because of how the SELECT statement works. the data we loaded into table game only contains information about American League games. This can be a serious problem. you may need to use ALL in a SELECT statement that contains a UNION clause. team WHERE home_team = team_name. you may be thinking. Informixuse the keyword UNIQUE as a synonym for DISTINCT. You will not need to use this keyword with a SELECT statement that stands by itself. As you recall.Listing 3−27: Omitting Duplicate Rows
SELECT DISTINCT home_team. The keyword ALL has the opposite effect: it tells the SQL engine not to throw away duplicate rows.
This outputs the following:
Angels Angels Angels Angels Angels Angels Angels Yankees White Sox Twins Tigers Royals Red Sox Rangers
As you can see. visiting_team DESC.
Outer joins
Consider the script in Listing 3−28: Listing 3−28: Join Two Tables
SELECT DISTINCT home_team. the Cartesian product of tables game and team excludes the rows in team that describe National League teams.

An outer join in effect tells the SQL engine to diddle with the output of the Cartesian product so that it contains a row for every row in a given table. This section discusses some of the more commonly used syntaxes. When we join column home_team with column team_name. Fortunately. the SQL engine replaces column home_team with NULL to fulfill the outer join. So much for the good news. it would output something similar to this:
Angels Angels NULL Astros Athletics Athletics Blue Jays Blue Jays NULL Braves Brewers Brewers NULL Cardinals
The column to the left gives the value of column home_team. The asterisk goes to the left of the operator to indicate a left outer join. regardless of whether it could be joined to a row in table team. The rows that have no counterpart in the other table are extended with NULL. • A full outer join means that every row in either team or game appears in a row in the output. the types of outer−join would have these effects: • A left outer join means that every row in game appears in a row in the output. If we rewrote Listing 3−28 to use an outer join. Because game holds no data for National League teams.
Sybase
Left outer join
Sybase indicates an outer join by attaching an asterisk to the comparison operator used in the join_expression. regardless of whether it is joined with a row in the other table. outer joins greatly increase the range of queries that you can write. Right outer join The table to the right of the join expression is outer joined to the table to the left of the outer join expression Full outer join Combine both left and right outer joins. Types of Outer Joins Outer joins come in three types: The table to the left of the join expression is outer joined to the table to the right of the join expression. to the right of the operator to indicate a right outer join. and an asterisk on both sides of the operator indicates a full outer join. the column on the right gives the value of column team_name. • A right outer join means that every row in team appears in a row in the output. regardless of whether a row in either could be joined to a row in the other. SQL2 gives us a way around this problem: the outer join. The bad news is that the notation for outer joins varies wildly among database packages. the following is the SELECT statement from Listing 3−28 using a Sybase−style left outer join: 98
.something did occur. regardless of whether it could be joined to a row in table game. For example. Notation of outer joins As you can see.

team WHERE home_team *= team_name. instead of an asterisk. team_name FROM game. team WHERE home_team *=* team_name. team_name FROM game. The terminology left outer join and right outer join are not very descriptive when applied to the Informix notation. Informix
Informix is yet another notation: it indicates an outer join by inserting keyword OUTER into the FROM clause. but it places that symbol after the table that is to be NULL extended. team_name FROM game. team WHERE home_team = team_name (+).SELECT DISTINCT home_team. team_name FROM game. team_name FROM game. rather. For example. the Informix notation can indicate a full or a partial outer join.
The following outer−joins game to team:
SELECT DISTINCT home_team. but using a right outer join:
SELECT DISTINCT home_team. the following rewrites Listing 3−28 to outer−join table team to table game using Informix notation:
SELECT DISTINCT home_team. team WHERE home_team (+) = team_name. but using a right outer join:
SELECT DISTINCT home_team. but using a full outer join:
SELECT DISTINCT home_team. but using a full outer join:
SELECT DISTINCT home_team. In effect.
And the same again. the following is the SELECT statement from Listing 3−28 using a left outer join:
SELECT DISTINCT home_team. team_name FROM game.
The same. team WHERE home_team =* team_name. team
99
. team WHERE home_team (+) = team_name (+). OUTER team WHERE home_team = team_name.
And the same again. team_name FROM OUTER game. OUTER prefixes the name of the table to be outer−joined.
The same. Oracle
Oracle uses an entirely different notation: it uses a parenthesized plus sign in the join_expression. Oracles notation reverses the notation used by Sybase. For example. team_name FROM game.

And the same again. whereas the Oracle and SQL−Server notations let you outer−join a table to some tables. that some database packages do not support outer joins. and not to others.team_name FROM team LEFT JOIN game ON team.home_team.
The Informix notation marks outer joins more clearly than does the notation used by Oracle or SQL Server. but implementing a full outer join:
SELECT DISTINCT home_team. too.
Each of the notations for outer joins has its strengths and weaknesses.team_name = game. if you prefix a table with OUTER. too.visiting_team = "White Sox" ORDER BY team_name. We do not describe this clause in detail. PostgreSQL first released support for outer joins in the winter of 2001. the notation is less specific: that is. You can follow the JOIN clause with a WHERE clause that further restricts the query.
Note that we inserted the clause LEFT JOIN to define the left outer join between tables team and game. this is one of the biggest limitations in porting SQL from one database package to another.team_name = game. team_name FROM OUTER game. that we excluded table game from the FROM clause. Clearly. It implements the keyword JOIN.home_team ORDER BY team_name. if we had included game in the FROM clause.home_team WHERE game. the MySQL parser would complain of a syntax error. Informix outer−joins it to every other table named in the FROM clause. however. On the other hand. The biggest weakness of each.
MySQL
MySQL uses a peculiarly convoluted notation for outer joins. team. We must note.
100
. team. Listing 3−30 adds a WHERE clause to Listing 3−29 to limit output to games in which the visiting team is the White Sox: Listing 3−30: Adding WHERE
SELECT DISTINCT game. For example. the script in Listing 3−29 rewrites Listing 3−28 to use a MySQL−style left outer join: Listing 3−29: MySQL Left Outer Join
SELECT DISTINCT game. Note.home_team.WHERE
home_team = team_name. In particular. is that none is recognized by any other package. OUTER team WHERE home_team = team_name. with which you can define the join. most editions of PostgreSQL that are in use on Linux systems do not support outer joins at all.team_name FROM team LEFT JOIN game ON team. however.

the White Sox). SUM(visiting_team_runs). ] FROM table_name [. SUM(home_team_runs) + SUM(visiting_team_runs) FROM game WHERE home_team = White Sox. practically every database package implements the following functions. However.Functions
As we noted at the beginning of this section. the expression
SUM(home_team_runs)
counted the runs the home team scored (in this instance. Another item that can be included in column_name clause are functions. the mean) of the column given it as an argument. (Some functions take multiple arguments. ] [ ASC|DESC ] ] [ UNION SELECT select_statement ]
Relational−database packages implement different suites of summary functions. SUM(). We also mentioned that it can include constants and arithmetic expressions. AVG() Summary function SUM() adds up the contents of the column given it as an argument. we discuss several examples later. A function is a block of code that is executed by the database engine and that returns a single value. the column_name clause of the SELECT statement can include items other than the names of columns. Summary function AVG() gives the average (that is. Most functions take one argument: the name of the column whose data are to be analyzed. When we take summary functions into account. and the expression
SUM(home_team_runs) + SUM(visiting_team_runs)
returned the sum of all runs scored by both teams. for example. the expression
SUM(visiting_team_runs)
counted the runs scored by the visiting teams. Listing 3−31: SUM() Function Output
SELECT SUM(home_team_runs).
The output is:
353 280 633
As you can see. the script in Listing 3−31. We present them as MySQL implements them. ] [ WHERE [ restrict_expression ] [ join_expression] ] [ ORDER BY column_name [.) Consider. which demonstrates the output of the summary function SUM(). 101
. the syntax of the SELECT statement appears as follows:
SELECT [ DISTINCT|ALL ] column_name | constant | arithmetic_expression | \ function ( column_name ) [.

whereas COUNT(*) counts the rows without regard to any given column. as you would expect.5541
MIN().7703 3. these two functions behave exactly the sameeach counts the number of rows that the SELECT statement generatesso there is no reason ever to use COUNT(). the maximum number of runs scored against them at home that season was 11. COUNT(). MAX(visiting_team_runs) FROM game WHERE home_team = White Sox.7838 8. Listing 3−33 demonstrates these functions.
This returns:
0 0 19 11
The minimum number of runs scored by either home team or visiting is zero.
102
. The maximum number of runs the White Sox scored in a game at home was 19. We will limit our examination to COUNT(*). AVG(home_team_runs). COUNT(*) The summary functions COUNT() and COUNT(*) count the number of rows generated by a given SELECT statement. AVG(visiting_team_runs). AVG(home_team_runs) + AVG(visiting_team_runs) FROM game WHERE home_team = White Sox. These two forms of counting differ in that COUNT() takes a column name as its argument. It gives the minimum and maximum values scored by the home and visiting teams when the White Sox were at home. However. MAX(home_team_runs).The script in Listing 3−32 extends Listing 3−31 to demonstrate AVG(): Listing 3−32: AVG()
SELECT SUM(home_team_runs). Summary function MAX() returns the maximum value in the column passed to it as its argument. MAX() Summary function MIN() returns the minimum value in the column passed to it as its argument. SUM(home_team_runs) + SUM(visiting_team_runs). SUM(visiting_team_runs). MIN(visiting_team_runs).
Its output is:
353 280 633 4. Listing 3−33: MIN() and MAX()
SELECT MIN(home_team_runs).

Syntax of groupings
The syntax of the GROUP BY clause is exactly like that of the ORDER BY clause: you can follow the keywords GROUP BY with the names of one or more columns. consider the example program in Listing 3−34. You could write 26 SELECT statements.
And the answer is:
5
That is. the syntax of the SELECT statement appears as follows:
SELECT [ DISTINCT|ALL ] column_name | constant | arithmetic_expression | \ function ( column_name ) [ . the summary functions can be quite useful when you wish to generate a simple summary of the rows within a table. which counted the number of times that the White Sox were shut out at home. GROUP BY clause As you can see. Now suppose that you want to know how many times every team was shut out at home. that you wanted to summarize only a subset of the rows of a table? Is there a way to do that with a summary function? The answer is yes. The SQL engine groups its output by the values of the columns. or you could use a GROUP BY clause to tell the SQL engine to group together each teams games and count each group individually. each of which is summarized individually by a summary function. ] ] [ ORDER BY column_name [. suppose you wished to know how many times the White Sox were shut out at home.You may wonder what use it is to know the number of rows that a given SELECT statement generates. Suppose. one for each team. the White Sox were shut out at home five times. there is a way. however. most of which begin with the phrases "How often ?" or "How many ?" For example. ] [ WHERE [ restrict_expression ] [ join_expression ] ] [ GROUP BY column_name [. ] FROM table_name [. and then invokes each summary function that youve named in the column_name clause for each of the subgroups so generated. The answer is that this information can answer a wide range of questions. in the order in which you name them. The GROUP BY clause enables you to organize the output of a SELECT statement into groups. ] [ ASC|DESC ] ] [ UNION SELECT select_statement ]
For example. The script in Listing 3−34 uses COUNT(*) to find the answer: Listing 3−34: Shutouts
SELECT COUNT(*) FROM game WHERE home_team = White Sox AND home_team_runs = 0. The script in Listing 3−35 does this: Listing 3−35: COUNT(*) and GROUP BY 103
. When we take summary functions into account. Commas must separate multiple column names.

However. you cannot put the COUNT(*) function into the ORDER BY clause. home_team is column 1. after all. In Listing 3−36.
104
. COUNT(*) FROM game WHERE home_team_runs = 0 GROUP BY home_team.
The output is:
Angels Athletics Blue Jays Brewers 5 4 4 1
You can combine the GROUP BY and ORDER BY clauses. Listing 3−37 sorts by the count of shut outs: Listing 3−37: Descending Order on an Expression
SELECT home_team. A columns number is determined by the order in which the columns are named in SELECT statements field_name clause. the script in Listing 3−36 generates the same output as Listing 3−35 except that the output is in descending order: Listing 3−36: Descending Order
SELECT home_team.SELECT home_team. and the output of the function COUNT(*) is column 2. SQL lets you use the number of a column clause as an alias for the columns name in GROUP BY and ORDER BY clauses. it can be doneif we use an alias for a column name. For example. COUNT(*) FROM game WHERE home_team_runs = 0 GROUP BY home_team ORDER BY 2 DESC.
The output is:
Yankees 3 White Sox 5 Twins 5 Tigers 4 Royals 5
Aliases for columns
At this point you may be asking whether there is a way to order the output of this SELECT statement by the number of times the team was shut out. This method enables you to identify a column that does not have a name because it was built by an expression or by a function. not by the name of the team? This is a real problem. COUNT(*) FROM game WHERE home_team_runs = 0 GROUP BY home_team ORDER BY home_team DESC. For example.

and other. These include trigonometric functions. Other functions In this section. IFNULL() lets you set what the query returns should a given expression be NULL. most database packages offer a rich set of functions. use the keyword AS. To assign a name to an expression. and the second argument is the value to be printed should the first expression evaluate to NULL. the script in Listing 3−38 rewrites Listing 3−37 to use a string as an alias for the COUNT(*) function: Listing 3−38: String Alias
SELECT home_team. COUNT(*) AS shutouts FROM game WHERE home_team_runs = 0 GROUP BY home_team ORDER BY shutouts DESC. then the second argument must be a number. Another way to use aliases is to assign a string as an expressions name. This ability to alias an expression comes in very handy as you begin to write complex SELECT statements. functions that format date and time data. if the first argument is an expression that outputs a string. For example. the clause ORDER BY 2 tells the SQL engine to sort the output by the contents of the second column. now we can easily see that the Rangers were the team that was shut out most often at home. we concentrated on the most commonly used functionsthose that summarize data for an entire column.
IFNULL()
One of the most useful of these miscellaneous functions is the IFNULL() function. functions that analyze or transform text. For example. whereas if the first argument is an expression that outputs a numeric value. which is the column built by the COUNT(*) function. then the second argument must be a string. The output is:
Rangers 7 Angels 5 White Sox 5 Twins 5
So. Listing 3−39 rewrites Listing 3−29 to use IFNULL(): Listing 3−39: Demonstrating IFNULL()
105
. miscellaneous functions. However. IFNULL() takes two arguments: the first argument is the expression to be evaluated. that is. but this script has the advantage of being more readable.Here. and then use that name throughout the rest of the SELECT statement. The type of the second argument must match that of the first.
The output of this script is the same as that of Listing 3−37.

home_team ORDER BY team_name. SQL also enables you to nest SELECT statements: an expression within a SELECT statements WHERE clause may itself be a SELECT statement. we described the UNION clause to the SELECT statement. Both PostgreSQL and MySQL support this feature. it enables us to easily perform tasks that would be difficult or impossible without it. the second argument to IFNULL() must also be a number.team_name.
Sub−SELECTs
Earlier. For example. consult the documentation that comes with your database package. −1) FROM team LEFT JOIN game ON team. When run. This clause enables us to link SELECT statements. These nested SELECT statements are not used often.SELECT DISTINCT team. unused value. the engine now prints −1. Adding new functions Many database packages let you code new functions and add them to the database engine. In most instances. Some database packages use the name ISNULL() instead of IFNULL().
Because home_team_runs is a numeric column. then you need to use IFNULL() to map NULL to another. team
106
. You could write a SELECT statement similar to the following:
SELECT home_team FROM game. some engines return zero if an integer column is NULL. For more information. if zero is a legal value in that column. however. the syntax and the behavior is the same. The method for coding a function and adding it varies quite a bit from one database package to the next. IFNULL(game. IFNULL() is particularly useful in cases in which a database engine returns an otherwise legal value to indicate NULL.home_team_runs. you must be a fairly accomplished C programmer.team_name = game. To take a simple example: lets say that you wanted to find the teams in the American League East that had been shut out at home. this script outputs the following:
Angels Angels Angels Angels 8 10 4 3
Brewers 0 Brewers 15 Cardinals −1 Cubs −1 Dodgers −1 Expos −1
Instead of printing the string NULL in instances where the database holds no game information for a given team. but they do let you answer some questions that would otherwise be difficult or impossible to answer.

the subquery is embedded within an IN expression in the WHERE clause. Now we examine how to modify the data that already resides within a database: either by deleting rows or by changing them. the team names that this subquery returns comprise the body of the IN expression. how to put data into it.WHERE
home_team_runs = 0 AND home_team = team_name AND league = A AND division = E ORDER BY home_team DESC
You could also do this with a subquery:
SELECT home_team FROM game.
SELECT: Conclusion
This concludes the introduction to the SELECT statement. but when you do use them. and how to extract data from it. The great majority of SELECT statements do not require a sub−SELECT. We give examples later. Congratulations for having come with us this far! You have now passed the most difficult and complex part of working with a relational database. Because a DELETE or UPDATE statement can modify only one table at a time. except to perform queries that can be performed in no other way. We do not claim that this section presented every facet of the SELECT. you have learned how to create a database. Note Not all database packages support sub−SELECTs. but what you learned here will enable you to perform the great majority of the selection tasks that you will need to operate your databases. Given that subqueries are by their nature inefficient. The most important exceptions are the SELECT statements that are embedded within a DELETE or (as we shall see) an UPDATE statement. each produces the same output.
Modifying the Data Within a Database
So far. The only difference is that the one that uses the subquery is significantly slower than the one that does not. These statements are not used often. the rest is downhill from here. team WHERE home_team_runs = 0 AND home_team IN ( SELECT team_name FROM team WHERE league = A AND division = E ) ORDER BY home_team DESC
As you can see. These two SELECT statements are equivalent. Believe it or not. a SELECT statement embedded within one of these two statements cannot use a join_expressionthe work performed by the join_expression must be replaced by a sub− SELECT. why should we use them? The answer is simple: you shouldnt. it is important that they be 107
.

fashioned correctly. We also discuss how SQL enables you to bundle changes into transactions. however. All logged changes to your database together comprise the body of the transaction. Under ANSI/ISO SQL. The syntax of the COMMIT statement is very simple:
COMMIT
And the syntax of the ROLLBACK statement is equally simple:
ROLLBACK
As you can see. the SQL engine opens a transaction. the SQL engine throws away all changes made since the beginning of the transaction. in which a user may assemble several inputs or modifications of the database. The input program will have no way of discovering this until it attempts to commit the transactionwhen one of the SQL statements fails. If you issue the SQL statement COMMIT. Mechanisms that are meant to preserve relational integrity may now begin to work against you when you try to repair your tables by hand. the SQL engine in effect makes a copy of the database for his input program. A crash at such a time can leave the database in a very confused state. because more than one person is racing to put 108
. Another problem that can arise is when more than one user is entering data simultaneously. However. to help preserve the integrity of your database. Transactions in interactive environments Transactions are also important in an interactive environment. the engine logs all changes you make to your database into a temporary area. SQL transactions give you a means by which your input program can ensure the integrity of the data being entered before your database is modified. the input program throughout its transaction is working with the database as it was when the transaction opened. your system crashed. all of which must dovetail.
COMMIT and ROLLBACK: Commit or abort database changes
Lets say that while you were loading a file of data into your data. but they can also complicate matters. If any of the items are missing or erroneous. it opens a new transaction and begins the process again. If. during that time another user may have modified the database in a way that contradicts the information the user is entering during his transaction. In either case. when you begin to work with your database. you will have no easy way to determine just how much of the file you were loading had. been loaded. For example. The situation is called a race condition. among other things. the SQL engine copies all of its logged changes into the permanent database. you issue the SQL statement ROLLBACK. for no reason that the user can discover. Transactions will help you guard against this situation. none of the items should be entered into the database. in fact. During the transaction. a database application that manages reservations must prevent two users from simultaneously booking two different people into the same seat. Users can step on each others toes by making contradictory modifications to the database. Fortunately. When a user opens a transaction. transactions enable you to add changes to your database in discrete groups: you can check whether a change had the effect you wanted before you modify your database. ANSI/ISO SQL has a mechanism with which you can protect your database against erroneous or broken updates or inputs: transactions.

Relational database packages differ in this regard. If you use DELETE without its WHERE clause. The SQL statement DELETE. the statement
DELETE FROM team
removes every row from table team. This means that rather than piling changes into one huge transaction. Open transactions upon exiting Another problem that the SQL engine faces is what it should do if the program that is issuing SQL statements exits with a transaction open. deletes rows from a table. The WHERE clause introduces an expression with which you can identify the rows to be deleted. The WHERE clause lets you identify the rows to be deleted. Its syntax is as follows:
DELETE FROM table_name [WHERE expression ]
The FROM clause names the table from which rows are to be deleted. the problem of users contradicting each other will never go away entirely. if the program was shut down intentionally. Other engines simply roll back the transaction regardless of whether the input program exited intentionally or not. automatically commit every SQL statement unless you explicitly open a transaction. transactions should be small and discrete. the loser being the one whose data are rejected. and to make it easy to recover from such a problem when it does occur.mutually exclusive data into the database. Unfortunately. but you can work to reduce the number of times it occurs. expression is a standard SQL expression. on a multiuser system. as we described for the SELECT statement. if you wanted to delete all teams whose home cities names lie in the first half of the alphabet. however. Some engines will attempt to determine the programs state when it exited: if the program crashed or otherwise exited abruptly. you could use the following statement:
DELETE FROM team WHERE city BETWEEN A% AND M%
109
. Some commercial SQL packages. For example. as its name suggests. it will commit the transaction. The lesson is that transactions should be designed to lessen the chances that users will step on each others toes. the engine will roll back the transaction. including Informix. the following statement deletes from table team all teams in the National League East:
DELETE FROM team WHERE league = N AND division = E
Likewise. by default it removes every row in table table_name. For example.
DELETE: Remove rows from tables
The simplest modification you can make to a table in your database is to delete some of its rows.

like INSERT and UPDATE statements. You could confirm it by again typing:
SELECT home_team. This has saved many a user from blowing a gaping hole into the middle of his database. Consider. In particular.
You see nothing: the data in table game has been wiped out. the following enables you to delete from table game every game that involves an American League team:
DELETE FROM game WHERE home_team IN ( SELECT DISTINCT team_name FROM team WHERE league = A )
Deletions and transactions Deletions. you did not make a backup. MySQL does not support transactions unless transactional support is specifically compiled into the MySQL engine. You began to type the following statements:
DELETE FROM game WHERE home_team = Angels. the keys are close to each other).
Despair! You have deleted every row from table game: the work of years of patient transcribing from The Sporting News is gone! (Naturally. the answer is simpletype:
ROLLBACK. not every database package supports transactions. while you have a chance. that you wished to remove every game from table game in which the California Angels is the home team. the WHERE clause of the DELETE statement can also contain a SELECT statement.
Voilà! That which was lost is now foundthe deleted rows are undeleted.. For example.
This returns:
Angels Angels Angels Angels Yankees Yankees Blue Jays Blue Jays
All is well again.) Unfortunately.) To confirm this horrible fact. then Return (after all. 110
. If your database package supports transactions. you type:
SELECT * FROM game. are controlled by transactions. for example. your finger slipped when you went to press the Return key at the end of the first line: by accident you pressed the semicolon .
However.As with the SELECT statement itself. (Now go and make that backup. and so by accident issued the statement:
DELETE FROM game. visiting team FROM game.

for example.
UPDATE: Modify rows within a table
The last major SQL statement that we consider is UPDATE. UPDATE game SET home_team = Highlanders WHERE home_team = Yankees. To do so. We did this to avoid violating referential integrity. The SET clause names the columns that are to be modified. The WHERE clause introduces an expression that enables you to define which rows are to be updated. SQLs ON DELETE clause lets you determine whether the deletions will cascade through the database. that the New York Yankees decided to change their name to the Highlanders (which name the team had before World War I). However.Deletions and relational integrity When we discussed the CREATE TABLE statement earlier in this chapter. COMMIT. UPDATE game SET visiting_team = Highlanders WHERE visiting_team = Yankees. MySQL does not implement this feature of SQL. COMMIT.
A few points in this script should be emphasized: • We inserted a new row into table team to describe Highlanders to the database. E). New York. • We used the COMMIT statement to commit the changes to our database after each INSERT or 111
. or bar the deletion should integrity be violated. we noted that some implementations of SQL let you set the default action that the engine should take when a deletion violates relational integrity. as table game has two foreign keys that refer table team. For example. you would use this script:
INSERT INTO TEAM VALUES ( Highlanders. Highlander Stadium. You can use an expression to define the value to which each is to be set. DELETE FROM team WHERE team_name = Yankees. the UPDATE statement modifies every row in the tableassuming that it does not violate any of the referential integrity clauses you entered when you defined the table. Suppose. This statement modifies the contents of a row or rows within a table. If this clause is not used. the deletion of a row from table team would be controlled by how we had set the ON DELETE clause for the foreign keys in table game. COMMIT. and the value to which each is to be set. set any referring foreign−key columns to NULL. column_name = expression ] [ WHERE expression ]
table_name names the table whose rows are to be modified. A. if it did. The syntax of this statement is as follows:
UPDATE table_name SET column_name = expression [. the following statement
UPDATE team SET name = Old MacDonald
sets the last name of every teams name to Old MacDonaldshould you ever wish to do such a thing.

a view is stored within the database. then the numeric link is the better choice. we look at views. This can be any form of a legal SELECT statement. The optional column_name clause enables you to name each column within the view. ) ] AS SELECT select_statement
The view_name gives the views name. but in this instance. This view prints the total number of runs scored by a given team at home. the Houston Astros were originally named the Colt . • If we had used a unique number to represent a team. it resembles the SELECT statement. the UPDATE statement is used to repair or complete an individual record. It has the following syntax:
CREATE VIEW view_name [ ( column_name [. Listing 3−40 builds a view and executes it. we preferred to save the output of each statement individually. In effect. We discussed views briefly in Chapter 2. instead of the teams name itself. use the statement CREATE VIEW. but now we explore them in a little more detail. as its name implies. In this. teams do change their names from time to time (for example. More often. Listing 3−40: A View
CREATE VIEW home_team_runs AS SELECT home_team. if we expect team names to change with any frequency at all. The AS SELECT clause identifies the SELECT statement with which data are selected from the database. However. i . the following statement repairs a score that is (or rather. The name must be unique for the database within which you are creating it. the same as if it were the name of a table. simply embed it within the FROM clause of a SELECT statement. then updating the name of a team would not be a big dealall we would have to do is change the name of the team in table team. a view is a SELECT statement that is stored within the database.45s). and all would be well. However. in this. To create a view. In this database.UPDATE statement. A view. should have been) erroneous:
UPDATE game SET visiting_team_runs = 7 WHERE home_team = Padres AND game_date = 10−7−1984
Views
As the next stop on our nickel tour of SQL. SUM(home_team_runs) FROM game
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. Such mass modifications are performed only rarely. we did not use a unique number to link the tables because in fact team names almost never change. For example. lets the user view a body of data within the database. To use a view. It may have been wiser to wait until all statements had executed successfully before we committed the changes to the database. For example. it resembles a table. • Only when a new team had been added to table team and all modifications made to table game do we remove the record that describes the now−obsolete Yankees.

For example. Stored procedures are useful because they let you move into the database the routines by which the database itself is accessed. However.
Views are useful for letting users passively view data. or it can mix the two. and which is executed when a given table is modified. These scripting languages vary wildly among vendors. SELECT * FROM home_team_runs. Not all database packages support views. we conclude our introduction to SQL. most database packages do not yet support this feature. if you intend to move a database from one database package to another. you can use a trigger to update the database automatically. then bear in mind that all of the code with which you implemented your stored procedures and triggers has to be rewritten. The code that forms the body of the trigger can be a script of SQL statements. Thus. and these differences make SQL scripts difficult to port from one implementation to another. just like the summary functions that are built into the SQL engine. then update a log or send mail to the database administrator. both in their power and in their syntax. however. if a given condition occurs within the database. However. and its disadvantages and advantages. They also make it much easier to write a complex SELECT statement. They are also used for building sets of data that can be downloaded to other programs (for example. in particular. or perform other useful housekeeping tasks.GROUP BY home_team. standard language for interrogating relational databases. row is used in place of tuple. A stored procedure is a function that is stored within the database. to enforce referential integrity. and table is used instead of relation. E. F. spreadsheets or applets) for further viewing or manipulation. Codd stated that a truly relational database must permit updates through views. to bump counters. except that a stored procedure may return more than one column. The discussion began with the history of SQL. As you may recall from Chapter 2. We make further use of views later in this book. or it can be a shell script. This is by no means an exhaustive discussion of this complex and useful language. In some instances. the standards that define SQL. you now know enough to perform most query tasks with SQL. Triggers and stored procedures usually are written in scripting languages that are created by the database vendor. A trigger is a portion of code that is stored within the database. no two implementations of SQL are exactly alike. MySQL does not support them. triggers can also be used to interact with programs outside the database.
Stored Procedures and Triggers
Stored procedures and triggers are the final topic for this chapter. You can use a stored procedure just like a summary function. On this note. for example. although no doubt you will need practice before you feel comfortable with it.
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.
Summary
This chapter introduces Structured Query Language (SQL). The terminology of SQL varied a bit from that used in relational theory: column is used as a rough equivalent of attribute. SQL is most useful as a reasonably powerful.

In particular. Triggers are SQL expressions that are stored within the database. We then examined each basic SQL statement in turn: • CREATECreate a database. if statements. SQL is not case sensitive. if a column holds an attribute that is numeric and has 355. you must use type INTEGERtype SMALLINT will not be able physically to hold every member of the domain. SQL recognizes data types that encode text. • ROLLBACKThrow away all changes made since either the beginning of the program. or the last COMMIT or ROLLBACK statement. For example. SQL usually is embedded within another program or language such as in a SQL interpreter or in a program written in another language (for example. • GRANTGrant permissions to a user on a given database or table. and functions. • UPDATEModify one or more rows within a table. or an index. two rules apply: The data type must be able physically to hold every value within the columns domain. • COMMITCommit changes to the database. it does not include many features of a general−purpose language.SQL is a query language rather than a fully featured programming language. Views are SELECT statements that are stored permanently within the database itself. binary numbers. just like the columns of a table. The assignment of data types to the columns within a table requires some thought. • INSERTInsert rows into a table. or ways to manipulate or redirect input or output. SQL recognizes a large number of keywordsthe exact number varies from standard to standard and from implementation to implementation. just like the summary functions that are built into the SQL engine. Stored procedures are functions that are stored within the database.
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. constants. For example. a table. • SELECTSelect data from a database. time. money. such as loops. and specialized data (for example. if a foreign key references a column that is of type INTEGER that key must also have type INTEGER. dates. including operators. and which are executed when a given action is taken upon a given table or tables. • DELETEDelete rows from a table. The data types of a column that is a foreign key must be exactly the same as the data type of the column in the table to which it is linked. The discussion of the SELECT statement also introduced the subject of SQL expressions. and binary large objects). The columns of a view can be included within another SELECT statement. C or Java).000 members.

To paraphrase General Dwight D. which is the relational query language used almost universally by relational databases. Planning the tasks for reaching the desired goal given the existing situation
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. Reality has no respect for the ideal. In Chapter 3. timing. but it does have to be accepted.Chapter 4: Designing a Database
Overview
In Chapter 2. Each component needs to be completely understood by the entire project team. That being said. we emphasize what you need to do to execute a project successfully within a real−world organization. The first section discusses how to plan and execute a database project. an uncommitted business sponsor does not accept anything but its own opinion. articulates the desired goal. We discuss how to translate a real−world problem into a set of tables that manage your application properly. Here. The third componentPlanning the Tasksdoesnt need to be intimately understood by the business sponsor. A committed business sponsor embraces a proven methodology. The three components are: 1. Using a proven. Eisenhower: Dont confuse the plan with the project. consistent recipe for planning and executing a project is frequently referred to as a methodology. establishing the reason or reasons why change is needed. A dependable. cost versus time.
What is a methodology and why have one
A methodology is a sequence of tasks structured for a desired outcome particular to an art or science. Describing and understanding the existing situation 3. integrity. and cost. Defining and understanding the goal or desired outcome 2. In this chapter. a word to the wise is appropriate. The second section discusses the art and craft of database design. we discuss how to execute a database project. It provides a way to box a project in terms of cost. and provides the route and milestones that guides the progression to reach the goal from the existing situation. relations. A good methodology provides a clear picture of the present situation. or at least does not commit to the effort to adequately plan the project. we discussed data. we introduced IBMs Structured Query Language (SQL). A practical methodology for a developing a plan A methodology for a developing a viable database project plan has three components. query language. or just time. dependable method for planning and executing projects results in better control over achieving goals. Having something you can refer to and use as a methodology goes a long way toward ensuring a usable project plan and increases the likelihood of efficient project execution. A comprehensive project plan has little bearing on the actual project progression. The chapter is in two sections. The future has no respect for the present.
Planning and Executing a Database Project
There are two critical steps to a successful database project: planning the project and executing the project. and the other features that comprise the relational model for databases.

never define a task that depends on two people simultaneously. or perhaps one. With a careful assessment and clear understanding. and have a task (or design) review at that milestone. system.
The goal statement
Not getting a clear. You will need to identify the roles (the grouping and classification of the skills) that the project will need before you can figure out which people will fill the roles. something to give it a purpose. though. Regardless of whether you think of the business rationale as the strategy for the business vision. It enables the plan to be efficient and to avoid consuming time. and there is a real danger of them becoming blame−storming sessions. A poor (ill−chosen. there are numerous obstacles to a successful project. A well−defined goal gives vitality and purpose to the project. A project is a tactic and there has to be a rationale for using a tactic. or of the business strategy as the rationale for the project.Defining and understanding the goal
An organization needs a vision. unambiguous articulation of the desired goal is an easy error to make. Create a new order−entry system on time and under budget an 116
. automating some business processes because they are consuming too much time when done manually frequently means that the processes are broken and not that they are too slow. the project is really the. or nebulous) goal consumes resources that are better used elsewhere. However. it is possible to know what the plan should consist of. This goal component is critical because it gives a reason for the existence of the project. If at all possible.
Describing and understanding the existing situation
A useful technique for defining the goal is to assess the existing environment.
Planning the tasks
This is where you connect the assessment and understanding of the existing situation with the goal. Not all of them are in the details of the project progress. A vital part of understanding the existing situation is to discern what problem a potential project can solve and what problem it cannot solve. or at least feel like it to the person whose milestone is being analyzed. assessing the existing situation is also one of the two ingredients of the plan. if at all. a software project computerizes a really bad business process. When you can put down on paper the problem(s) created by the existing system (sometimes called feeling the pain) and how this situation prevents the business from executing on its business strategy and therefore fulfilling its vision. Youll probably find tasks that can occur in parallel. For example. These milestone reviews must be productive. Too often. Impediments to a successful project As you might expect. Break the plan into tasks small enough that your available resources can accomplish them. what does a clearly stated goal look like? Isnt stating. ill−defined. Putting a strategy into action is done through tactics. you have the goal and rationale for the project. material. It is always helpful to just mull over the results in a group. which just moves the problem down the line. tactic for implementing the strategy. and work situation. either. This is another place where the project leaders and/or project champions are important for their attitude and ability to inspire and lead. preferably one person per task. To fulfill this vision requires a strategy. and people unnecessarily. We touch on just a few of the pitfalls that can be created before the project actually gets under way. Set a milestone for each task. defining just what it is that the organization does better than any other organization. After all.

This is exclusive of the remark above about what the organization will gain. One meeting where the project sponsors are in attendance should focus on the business processes that will change and what the impact of those changes will be. A third problem is having a project that is without a clear organizational advantage. The essential elements of a project are those requirements that bring the most return. or maybe a couple of meetings having different focus. This is manifested by: • A clear benefit to the organization • Realistic expectations on the part of the receivers of the project. It is impossible to have a successful project when the business goals are not clearly defined and stated. is the solution for this problem. Not getting a clear. and financing. needs. A successful project requires At a high level. A project kickoff meeting. These specifications are not even necessarily the technical/performance specifications. A clear goal would refer to the specifications that are agreed upon to be met. Not understanding the process for achieving that goal given the existing situation reflects a communication problem.articulation of a clearly understood goal? The problem is the nebulous nature of the phrase new order−entry system. is a problem if the organization cannot select vital projects. This is an ongoing effort. Setting realistic expectations is an often−overlooked key to acceptance of the completed project. A second meeting with the project team should focus on the architecture of the project. Dont let it get to the point of I thought it was going to . Competition among several projects for limited resources. personnel. A lack of focus on the part of project sponsors and project managers will kill a project by neglect and lack of support through difficulties. One of the first responsibilities of the project sponsor (and a project leader) is to keep changing or unrealistic expectations in check. The result is an unsuccessful project. This can be the result of not understanding the organizations goals. the project goals. and the project deliverables. or by a thousand small changes. A project/organization that cannot distinguish among its musts. then the project will fall short of success. that is. the tasks. and the people paying for the project 117
. Unrealistic expectations always kill a project. and agreement on the need and the importance of meeting that need. or how the project fits into the organizations overall strategy. If achieving the project goal is not within the capability of the organization. What is meant here is that the organization must gain something from the project that clearly increases (or improves) the delivery of the service or product that it produces. See the section on Change Control/Management for related problems. it should never cease. unambiguous understanding of the existing situation will inevitably lead to proposing and providing a solution that does not sufficiently address (solve) the problems that the organization is dealing with. a successful project needs support. and bad feelings all around. A second problem with even a clear goal is the question of whether the goal is achievable. or that the organization has unrealistic expectations of what it takes to complete a project successfully. No prioritization of competing goals presents problems with projects because it means that the organization is either unable to decide which projects are the most important and therefore should get allocated the limited resources. what is to be gained by the organization. and wants cannot focus on the essential elements of a project. This is another symptom of an organization that cannot prioritize. however well planned each may be.

• A project champion who maintains visibility. As another example. and from the difference. although communication is everyones responsibility. so this should be considered as some of the ongoing project tasks and a resource should be assigned responsibility for change management. there is a need for change control in a project. the project plan as a document becomes much less useful. you should use the foregoing list as part of a checklist for gauging the project risk.
Getting to first basePhases and components of the plan
A project plan should consist of some or all of the following: • Business problem definition • Proposed solutions with a cost/benefit analysis of the proposed solutions • Chosen solution and rationale • Project objectives and organization • Project team makeup with major organization representatives • Critical success factors (dont overlook these!) • Project scope • Project planning assumptions • Detailed project plan and milestones • Project risks and issues • Project contingencies The idea is to plan well enough that the project participants know. This is true especially for pet projectsfor example. This should be developed as part of a planning cycle that looks at the present state of the organization. the more likely that the project will proceed. honest (honest!) communication • Focus • Change control and management of requested changes • Timely access to resources • A willing acceptance of the results • An end Although youll rarely find all of these elements present. it is especially the responsibility of the project leader. identifies the needs of the organization. for example. The more that the pressure is outside the control of the organization. and include: • Regulatory compliance pressure. The pressures for an organization to change originate in a number of places. Establishing the need of the organization The very first bit of information thats established is the organizations need for a project. department initiated projectsas compared to projects that are mandated by higher levels 118
. For example. compares it to the desired state of the organization. Some of these points need to be part of the project plan as the responsibility of a project role. and agree with the goals and the process. enthusiasm. understand. After the plan is complete and the project gets underway. collecting new state and local taxes • Competitive pressure • Organizational efficiency • Market pressures for new products You should make it a point to know the pressure for the project. focus • Clear. Establishing the need is part of the diagnoses.

Analyze the responses so that you can understand and convince anyone that you understand the issues about the organizations perspective of the project. and the business areas that may be waiting their turn. Putting together a list of questions for a questionnaire The best way to get this information is to write down as many questions as you can think of that have to do with the organization.
Evaluating and analyzing the organizational environment
This is part of the diagnosis of the problem. if at all possible. Knowing this will aid your communicating in a meaningful way with the project sponsor. this problem? • Are there internal or external factors that could cause the problem to get worse or go away? • Are there advantages to leaving well enough alone? • Can you name the parts of the organization that are affected by the problem? How about the unaffected areas? Who has the biggest stake? • Do you see a downside to addressing this problem now? What makes this a particularly good or bad time to address this problem? • Do you think that the organization is prepared to solve this problem? (The answer to this question can be very revealing!) What might work against efforts to address this problem? • Could you suggest what unintended side effects the organization might experience as a result of 119
. higher than even the project sponsor. for example. Get the person youre interviewing to give their definition of the problem. order fulfillment errors. You may not be able to make this choice. What you really want is to get unrehearsed answers from people high up in the organization. It could be that one of these projects becomes more important even before your project is complete. By analyzing and comparing responses. • Has the organization. but you should be aware of. you should be able to develop a history from the answers. and how did it become apparent? • Can you give me your perspective on the current business process? What problems have resulted from this? • What do you expect to gain (or lose) by solving this problem? • How do financial factors contribute to this problem? • Who else are you aware of who has also addressed.in the organization. as well as identifying those people who are unconcerned. maybe even antagonistic. and use that definition when you talk to them. You need to understand what will solve the problem. you will be able to discover any discrepancies between attitudes and expectations at the highest level of the organization as compared to the project level of the organization. or you. what other projects similar to this project existed at the time and why this one was chosen over them. even solved. Where you see the word problem or issue in the following questions. what is your perspective on the results? Where they good or bad results? Was your expectation fulfilled? • How does this problem make you lose sleep? • When did this problem become apparent to you. toward the project. Knowing the driving force for the project enables you to identify the people who have the biggest stake in seeing that the project is successful. Dont be surprised to find that there are underlying organizational issues that should be solved before resorting to a technical solution. Establishing the relative benefit as compared to other needs of the organization This should be called the compelling reason to proceed. replace it with a statement of the actual problem. had experience solving this kind of problem before? If yes. and put into the project documentation. It also forms a part of the plan of action. You are looking for hidden pitfalls and hidden opportunities for success.

Where does the data come from and who supplies it? • Does it come from customers? • Does it come from suppliers. Keep a copy of the responses. internally? • How much of this is already captured in existing systems? Is there documentation for this? Is a new application definitely needed.
Project scope
Establishing the project scopethe extent of what is to be achievedshould come from questions and analysis of the responses. how has this been determined? • Is there an existing application that can be used as a model? • Does modifying an existing application look feasible? • Are there off−the−shelf solutions? How would they be integrated? Who would do the integration? Are there internal staff members who are knowledgeable enough to handle it? Is integration with existing systems needed because thats where the data will come from? • How many systems? How old are they? Are their interfaces proprietary? Can the data format be changed or does this project need to reformat/translate the data? • When will the interface specifications be available? Who do you get them from? Will it cost money? • Who will write the interfaces? Will it have to be planned into this project? Do you have to coordinate and integrate with concurrent projects? • When will the interface specifications be available? • Who will write the interfaces? Is this a departmental/location/and so on infrastructure improvement? • Are hardware purchases to be made out of the project budget? • What is the timing of the purchases? • Who is responsible for installation? • Is there a list of qualified vendors? • Has anyone already contacted vendors and made any commitments? What end−user software is needed? 120
.solving this problem? What do you recommend to avoid or to minimize them? Establishing the project with a plan This involves project plan and strategy. Establishing the strategy comes from knowledge of the kinds of solutionstechnical and organizationalthat are available and what the scope of the project is. governments. Add to this list and use it to formally put a box around the project.
Project plan and strategy
The project strategy and plan come after determining the gap. Dont ask technical questions of nontechnical people or youll have them designing the solution blindly. and project scope. Heres a list of questions that you can begin with. the difference between the existing situation and environment and the desired situation and environment.

Change control You need. Then.• How many users are there now? How many users will there be in one. some acknowledgment that things may change during the project. Use the following lists to help you start on the questions that you will need to ask. and three years? • Who is responsible for developing the end−user training? Who is responsible for conducting the end−user training? When will it occur? • Who is responsible for DBA training? When will that occur? Who will be trained? Is this enough considering the number of users and criticality of the system? Help Desk Staffing and Training • How many help desk people are needed considering the number of users? • Who is responsible for developing the help desk staff training? Who is responsible for conducting the help desk staff training? End−User Desktop • Are new desktop PCs going to be needed based on the quantity and age of the current systems? Are the existing desktop PCs adequate for the expected end−user software? How many users are there now? How many users will there be in one. Determining the hardware and software needs This is more information gathering. and three years? • Who is responsible for specifying the desktop PCs? Who is responsible for purchasing the desktop PCs? Who is responsible for installing and supporting them? Project Staffing • Are third−party consultants being used for development? Where will they sit? What computers and other equipment are required for them? • Who is responsible for which deliverables and when (doesnt require a lot of detail at this point)? • Does it generate management reports? What reports? Describe them! • Are there regulatory requirements? Please identify those that are applicable. at minimum. Some of the requirements may seem to jump out at you. two. but be sure that its not you just making presumptions about a solution before all of the investigation (assessments) is complete. at least put in a section that says. update your rsum.
Project hardware and software
Determining the needs of the project for either or both hardware and software require some design work to be done. and three years? • If any end−user software needs to be purchased. Planning is an iterative 121
. two. two. If you dont expect to be affected by changes. who is buying it? • Is it budgeted for in the departments where it will be installed? Training Issues • How many users are there now? How many users will there be in one. You should always be developing questions as you go. I dont have a reasonable expectation that any changes will impact this project. usually only at an architectural level (as opposed to a detailed level). It is especially helpful to make a list of the things that you want answered based on the rough scope that you developed earlier.

you need to ask about administration of the servers if youre using existing hardware. stopping only when asking questions begins to draw blank stares!
Computer/server
Although not a hardware question per se. does the architecture specify a client−server solution? Is there data to be accessed that resides on a mainframe? Is this a Web−based solution? Is this a server−only solution? Are you developing only the middle tier of a much larger project? Are you replacing an existing RDBMS and not changing the architecture? You can see from even this simple list that your questions need to be developed from the architecture.
RDBMS
Because this is a book about Linux databases. SCSI
Tape/tape backup
• Tape drive types. topology. Be very aware that database administration requires a different role than server administration does. which. protocols. • What is the licensing cost? What is the annual maintenance? • How much data is anticipated (this is for sizing the RDBMS) and what is its expected growth over 122
. for example. is developed from the strategy for solving the problem. in turn. wiring infrastructure • Is dial−up (remote) access available? • Is ftp available to other servers or to the outside world (maybe through a firewall)? • Are other Linux/UNIX workstations connected? Software needs The solution architecture will determine the direction you go here when looking at software. we provide just a few questions to get you started! Look at the chapters on specific databases for more questions. • Vendor and model number • Amount of RAM and type (is it error correcting?) • Number and type of processors • BIOS or Firmware version
Disk storage systems
• Number and size of disks • Disk types • Is a RAID (redundant array of independent disks) storage system attached? What is the RAID level? • What other disk drive interfaces/controllers are used • Controller types.practice. If you specify new hardware. that is. tape media • Tape drive capacity and speed
Operating system
• Linux version and vendor (be very specific) • Compiler version • Connectivity • Network configuration. For example. then administration will become an issue that youll need to cover in your plan.

is it fully ANSI SQL−92 compliant?
Middleware
If the high−level solution architecture is leaning toward a multitier solution. What you really need here from the solution architecture is what portions of the solution will be purchased and what will be developed. or will simpler static pages be used? • What HTML editors/Web−page development environment will be needed? • Are there graphical or image development and manipulation tasks? • Which browser will be used? • What Java version will be used? Java Beans? • Is a transaction monitor needed for distributed databases? Is one available for Linux? • What database−specific development tools are missing? Are ODBC libraries. too? Do you need one or more firewalls? Where is the database with respect to the firewall? (You can add a whole bunch more questions about Web servers!) • Will a mainframe be involved? Is mainframe connectivity an issue? If so.) Application development For application development. you will have to answer questions such as those that follow. or ODBC. PHP. to which system (machine type/database type)? (Add more gateway questions here. Even at a high level. youll probably have interfaces to existing systems. even software has interfaces) that will have to be spelled out in the design. Its pretty rare not to have this requirement. Java? For which portion of the solution will it be used? • Will CGI be used? • Are dynamic Web pages required by the solution. availability (or time to develop). it will get long if you have a multitier solution. the choice to buy or develop is readily apparent based on cost. Answer these following: • Which language development tools are anticipated: C/C++.one and two years? • Is data from an existing RDBMS being migrated? How will this be accomplished? Is there a bulk data−loading utility? How long will it take? • How is security controlled at the database level? • Does the RDBMS have backup utilities? How are they managed? Are there Database Administrators available to take on the additional work? • Who will administer the RDBMS (who will be the DBA) and what administrative tools are available? • What are the APIs for the RDBMS? Is a Java (JDBC). Between these are the interface specifications (yes. a high−level description of the application is needed. is there a Web server to be selected. JDBC classes. Perl. Even if youre purchasing a complete solution. You should be aware that there are only two choices for software: buy it or develop it. or Perl DBI. for example. or Perl DBI classes needed?
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. Although this list may seem short. • How will data access/security be controlled? Will it be through the application? • Is the database server to reside on an inner tier and will it be executing CGI? • If this is a Web−based solution. or C/C++ API available? Is CGI available? • What version of SQL is supported. if a database gateway is needed to access mainframe based data. and features.

Module description
Briefly describe the purpose (what part of the overall design) and primary functions of each module. This is not a language−specific document! This information along with the data−flow diagram shows how the program works.
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. Use the concept design documentation for design reviews. analyzing the impact of feature changes both to the schedule and the other functions. there is plenty of literature on system engineering (this subject).Implementation strategy and design
The design requires a conceptual design document followed by an application/process flow diagram. that is. or to a PC). It is helpful to begin with a diagram of showing/illustrating all the primary system functions and features and how they relate to each other. how the system functions are partitioned among the components of the design. Again. Ultimately. for example. Following those documents. Functional specification The following sections describe functional specifications. Concept design The conceptual design should provide the strategy for implementing the system functions. Make sure that these diagrams show all of the programs. the modules in which the functions are placed. Module logic−flow diagrams This document should outline the logic of the program. Use an agreed upon pseudo−code format to specify the logic within the module. tables. easily comprehended view of all aspects of the module. any software that is required can be specified by its place in the design and the work that it has to accomplish. Data−flow diagrams Data−flow diagrams show the flow and interaction of data through the application. From these lowest−level diagrams the entire system will have been specified and ready for implementation. you are comparing what has been implemented with the specifications. its specifications can be developed just as if you were purchasing off−the−shelf software. both theoretical and practical. dont write it in an actual programming language. it should provide a high−level. to be truly useful it should be easily comprehended. further breaking this down until the individual modules are shown. and interfaces to other systems affected by each modules. that is. This must agree with the module functional specification because it becomes part of the module functional specification. yet comprehensive. validates data according to business rules. provides a GUI object. The only difference is that you have to write it and support it! The methods and techniques for partitioning and specifying software at a more detailed level are left for you to research. It shows the data needed at each interface point in the system (where modules connect) and provides the guidance to determine the information and business rules required to process the data and pass it on to the next step. When you hold design reviews. you will have a functional specification for every module and subsystem in the design. implements security. To be truly useful. If custom software is called for. Dont get into syntax issues here. user output (to reports.

Database logical design: Entity relationship diagrams A reasonably experienced database designer. use this list as a starting point: Entity name Table name Column name Attribute name Column data type Nullable Default value Domain Description Data source The business entity that this table models. if its easily described). A description of how the column is used. From the logical design they can produce the physical design. select. wont you? A data dictionary The data dictionary is the document that defines the entities (tables). The physical design will change. for example. and representation of data. or a system engineer can develop the logical design by following industry practices and by using the information from all of this design documentation. the default value is for this attribute. A useful data dictionary contains enough information that a developer and database administrator can write correct programs that access the data without illogical results (that they make sense from a business perspective). as well as supply data to others. For now. and delete data without creating integrity problems. modifications of each input datum. The following sections in this chapter discuss database design in much more detail. The unique identifier for the table column. constant values. and length if the source is from a file and not a system. or decimal (10.2). create. and can modify. format. and so forth. for example integer. List every assumption. Describe in detail the transformations. update.Design strategy
Describe the approach used to create the module based on the higher level specifications. The system plus table plus column(s) from which this datum is gotten. volume of data. especially the data types/sizes. of course you will have design reviews of all of these changes. is it manipulated by using insert. The domain for this attribute (the range of valid values. and the like) the following information should be provided: data source physical name. attributes. the interdependencies among data. and so forth. data source type. primary key. The columns physical data type. Be especially diligent about side effects!
Database data sources
For each database data source (table. a DBA. file. 125
. validations. frequency of execution. It may give a filename. maybe relationships will change among entities or as new entities are identified. delete. and so on. char (10). too. What. if any. But. foreign key. made about the specification in addition to the interface specification (the input/output part). Plan for the logical design to evolve. The attribute (property or characteristic) of the entity being modeled by the column. position. Whether or not this attribute can be NULL and still be valid. and intertable and intratables relationshipsfor example. command line. return values.
Detailed specification
Proved a detailed functional description of the module based on the higher level specifications. The unique identifier for each table.

GUI layouts
A mock−up of the screen layout should be provided. navigation to other screens. Maximum input length. Confirmation upon validation. Validation rules (minimum and maximum values. The project architecture determines which roles are needed.
Report layouts
Report layouts are significantly easier than GUI design. There can be many more roles depending on the scope of the project. Business rules applied Shows how this value is derived or how this attribute value is used. so the application name should be provided. These are major roles that can appear on a database project. Button/check box/edit box type of interface element.It may give a variable name in a program if from an application. Cultivates and maintains sponsorship for mission critical initiatives. for efficient GUI design. the following. Cancel. Dependencies with other fields. The project plan determines when and for how long. and tab order from field to field. Maximum display length. User interface and report layouts It has been reported that user interface design ends up taking at least 50 percent of the total design and implementation effort. this number doesnt seem so outrageous. at a minimum.
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. Nevertheless. it is not necessary to find a person whose skill and experience exactly matches the role description below. Start with a mockup of the report and address the following: • Report header information • Report column descriptions • Field calculations • Sorting options • Printing options
People resources and project roles
There are project roles and there are people. People fill a role according to the task in the project. When planning a project. the project is divided into tasks that essentially map to individual roles. For each data item on the screen. reports are output only. every form must fit into a seamless flow for information entry. Primary roles The Director of Enterprise Information Architecture possesses insight into short and long−term business requirements and strategies. Default value. and so on). Creates and supplies the enterprise level vision and strategies. Calculations. The information should be readily comprehended. a detailed description that addresses. Also. You also need to user control and flow via such items such as buttons (OK. After all. The following descriptions are meant only as a guide for you to use. and the like). When you consider the amount of data validation that needs to take place for just about every data entry field on a screen for a typical interactive windowing application. is needed: Title/description. the report layout needs to be carefully considered so that the data is displayed so as to convey the maximum information in the least amount of time.

Skills: Is a people person (this person may be above you. Needs 127
. The Project Leader is directly responsible for the start−to−finish implementation of specific information system development projects. and training. project planning development and tracking. should be viewed as an expert. coordinates schedules and resources for design testing. Provides approval at project milestones. Contributes to the project plan. and client−server technologies is required. this role defines tactical and/or strategic data requirements and priority of information needs. May be responsible for end−user. excellent team−building and intrapersonal communication skills are needed. Skills: Hands−on end−user tool installation. Depending on the project. Should have taken training/certification offered by software vendors if an off−the−shelf solution is used. Skills: System development project management with a strong customer focus. The End−User Tool Expert manages all aspects related to the installation/configuration. articulating the problem to be solved. deployment. including external and internal project coordination. integrated with information delivery strategies that are consistent with organizational goals and experience. mainframe. resources. assigning responsible roles for the implementation. approves specifications as they develop and evolve. Has access to executives. Develops (the projects) system architecture. or for train the trainer training when that part of the project is reached. and is focused on results. assigns and coordinates the personnel resources for the project. and approves designs at design reviews Skills: Information system design expertise. Skills: Knowledgeable about the subject area. Contributes to the design and specification of the end−user tool(s). Has knowledge of existing systems and the people responsible for those systems. arranges for organizational experts needed by the project. in conjunction with other functional groups. has the ability to communicate clearly. schedules design reviews. scope. The IT Project Manager manages the organizations information system development projects. coordinates interviews. issue tracking. This person. Conducts. Skills: System development project management (presumes interpersonal and communication skills have been proven!). status reporting. acceptance testing. requirements. Consults with users on an ongoing basis for the duration of the project. resources. participates in. Substantial overall PC and Web skills are a plus. The System Architect possesses broad knowledge of computer and information systems and information delivery. especially for personnel resource assignment. a solid foundation in Web. The Sponsor Representative represents the goals of the project sponsor to the project. Provides end−user training in accessing and using the database. so you have no choice!). Provides reliable technical planning and control. and implementation. Should have current knowledge of emerging tools and techniques in information delivery. software development experience may be needed. configuration. and the effective utilization/implementation of all designated end−user software. Ensures that all projects are in accordance with organizations strategic efforts. Provides the definitions of business data requirements and business rules. Manages project definition. May develop user documentation and training materials. Has an understanding of the disparate project requirements for the varying user groups and the related source systems to ensure a cohesive strategy across initiatives. and so on. Because the person filling this role has the primary responsibility for the project teams functioning. and deliverables. validates correctness and completeness of the project strategy. Depending on the project. and has the perspective to relate to other information technology disciplines. As a primary receiver of the completed project.

data contents. Familiarity with data−modeling tools is preferred. and business rules. backup and recovery software. May need experience with mainframe data access. provides detail system knowledge. Skills: Solid technical skills on the source system platforms. performance monitoring. Skills: Extensive Linux/UNIX system administration experience. The Database Administrator (DBA) is responsible for all aspects relating to the installation. use. Tests and debugs programs and more complex systems. Keeps abreast of developments in information technologies. The Linux System Administrator manages all aspects related to the installation/configuration and utilization of all primary server related hardware and software (operating system. Contributes to the detailed design specification. and system interdependencies and interfaces is absolutely needed. programming languages. representing their needs. Because mainframes still are a distinctly different species of computer system from Linux systems. database utilities. works well with diverse personalities. including programming and data access experience. data requirements. Must also possess strong verbal. physical implementation strategies and trade−offs. Overall. needs a strong relational database knowledge. Directs the efforts of programmers. relationships. end−user database access. Skills: Linux RDBMS−specific design. is capable of clear written communication. The Programmer/Analyst understands and provides analysis and business processes. Also performs basic administrative tasks as required for end−user access at the operating system level. unique data characteristics. creates the data dictionary for the project and maintains the data dictionary after the project is complete. modeling. and serves as the primary contact/interface to mainframe system owners/support personnel. database security. and so on). overall database/application tuning. In conjunction with the Data Modeler. Extensive practical hands−on DBA experience. written. Knowledgeable about information system design. Provides project−level support by advising on and performing logical database design. Translates logical data requirements into a physical design. Coordinates and/or performs all physical server configurations modifications with regards to kernel OS modifications. network software/protocols. and backup and disaster recovery strategies. Because this role is one of the two best suited for creating the data dictionary. The Data Modeler analyzes the requirements and develops the logical data requirements project. Skills: Good oral skills. SQL language. strong analytical abilities. and computer hardware and software. it creates the data definitions. The End−User Liaison works closely with the end users. and has an understanding of how they accomplish their tasks. this role has distinctly unique purposes. business rules. The Mainframe System Programmer or Administrator ensures that mainframe processing performs as designed.extensive knowledge of the logical and physical contents of the database. Provides documentation to the rest of the project. and analytical skills. and general maintenance upgrades. expanding storage and memory capacity. indexing strategies. Conducts and evaluates results of interviews with end users and peers in other business groups to devise specifications for programs (software). Conversant in data−modeling theory and experienced in data−modeling practice. information flow. as well. configuration. Implements these specifications as program modules. A broad understanding of mainframe system(s) functionality. which is especially important when the 128
. Understands business processes. and monitoring of the Linux database software and/or the specific database. strong relational database knowledge with formal training. Skills: Overall.

processes are broken. Can communicate with end users, explaining and exploring alternatives, new business process and work flow. Contributes to the design and specifications of the end−user tool(s) for the project. Skills: Good oral skills; works well with diverse personalities; is capable of clear written communication. The Network Engineer keeps abreast of developments in network technologies; protocols, topologies, wiring (or wireless) application interfaces (for example, Web browsers), network performance, network solutions, analyzing trade−offs. Knowledge of the organizations network infrastructure. Skills: Education and experience in networking (design, installation, and maintenance) and computer communication. Customer resources The goal of obtaining personnel availability information is to ensure that all the resources needed to make the project successful are available for the duration of the project. These people, once identified, will be relied upon for critical project activities. Document any resource concerns, such as availability, experience, or suitability, that may adversely affect the outcome of the project. For example, concurrent responsibility for multiple projects by a key staff member that might interfere with this project. Use the following questions to evaluate your resources, whether or not they are internal (from your own organization) or are external (maybe a customers organization or an outsourcing firm). Add to this list as the project scope dictates. • Who is the project manager and how many simultaneous projects will the manager have? • Will there be a dedicated Linux system administrator for the duration of this project? • Will there be a dedicated DBA for the duration of the project? • How many (qualified) application/middleware/Web developers will be working on the project? What are their individual qualifications (list products, other projects, and so on) and their experience with such tools and languages as C, C++, Java, Perl, CGI/PHP, Web Servers (Apache), JDBC, RDBMS experience (design and programming) especially with Linux databases. • What will be the makeup of the test group that performs the system test? • Which, if any, system integrators will help with the development? How many people from the system integrator will be needed and are their qualifications available? • What support requirements are anticipated from other parts of the organization; for example, performance analysis and tuning, application migration, client tools?

Testing the system
System testing is driven by the system architecture. The System Architect is the person most responsible for developing the system test plan. From the system test plan, and the functional requirements come the test plans for the constituent elements of the system. The System Test Plan describes the procedure(s) for system testing, testing approach and philosophy for the system testing process. The System Test plan specifies the testing environment from a hardware and software perspective (which hardware platforms, networked in what way, which software operating systems and tools, configuration parameters, and so on). The testing environment needs to be kept constant so that no variables are introduced that are not part of the plan, creating unreliable and nonrepeatable results. All customer requirements must be addressed in the System Test Plan, one by one. Each requirement is 129

described and how it is tested and verified. Unusual test conditions need to be explained. Inputs for each test must be specified and what outcomes indicate pass or fail. Any particular preloading of the database and what this data signifies is also defined here. Bug tracking and identification are essential parts of this test plan. The plan must specify how this is accomplished and what the process is for regression testing once a fix is made. Testing the system components From the system test plan and the functional requirements come the test plans for the constituent elements of the system, usually referred to as a unit test. The system component developers (whether software or database or hardware) and the System Architect develop the unit test strategy, that is, what constitutes proof that the unit meets the requirements and that it functions without error. The unit test documentation should state the purpose of the test, the modules required, and the requirements to verify. From these the unit test procedure is developed. The test procedure specifies how the test is conducted and what constitutes success. Final acceptance testing The final acceptance test is developed with the help of the System Architect, the Business Sponsor, End−User Liaison, the Project Manager, and Project Leader(s). Needless to say, this is the acid test for the project. The final acceptance test specifies the proof that is needed for the project to end and the users take it over. In the final acceptance test plan, the system and software configuration and scenario necessary confirm that the system meets the needs of the users. Typically, the scenario is a scripted business process using real−life data.

Change control
Change happens, you just dont want it to happen to your project. However, change requests will seem like a blizzard by the time you reach the testing phase. The best strategy is to assume that a change can be valid, it just has to have the support of the project sponsor. Probably the most difficult changes to manage are those that come through the sponsor or the sponsors liaison. The implication is that you cannot refuse them because they should be easy to do . Youll need to treat these especially carefully, meaning that you have to be diligent in documenting why these are a really bad idea. Objectives of change control Unless the requested change is to eliminate features that were going to consume an inordinate amount of resources, changes will at least make the project take longer. This doesnt mean that change is bad; just that change is, well, time−consuming. What you really want is to make sure that the only changes that are implemented are those that (a) fix a bug or correct an error in the specifications that prevents the project from meeting its (prioritized) goals and those that (b) are fully funded. Essentially, the change control team must make sure that the benefits clearly outweigh the costs of the change. Be on guard for death by a million small changes making things better. So, youll need criteria to help the change control team evaluate the change requests in a timely and efficient manner. Here is a list of questions to which youll need the answers for each proposed change.

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Change evaluation criteria Where did the change request originate? Does it reflect a strategic change of the organization? Is the requested change outside of the project scope? Would it change the justification for the project? Is there valid justification included in the request? Has there been written approval from the sponsor provided? In what way is the change essential to the project at this time? What is the risk to the project by not going ahead at this time? What is the impact to the project plan? What is the quantified cost and schedule impact? Make sure that the cost considers the diversion of resources from other tasks. Does it save time, money, or resources? How does this change affect the critical path? What would the side effect be if this change is implemented? Are other systems or projects affected by this change, dependent on it, adversely affected by it? Have the other change control team(s) been made aware of this change request? Have they made a decision?

Planning for the operations manual documentation
Regardless of whether or not the project will be supported internally, a users operating manual is necessary. You should think of this manual as having all of the information necessary to install, configure and run the system as delivered. This includes requirements for operational support, hardware requirements, software requirements, network configuration, software installation, and hardware installation. It should be comprehensive, even to the point of including information that is easily obtained elsewhere. Nothing that is obvious to the project team will be obvious to those who follow. You can consider the manual as a receiver for all of the procedures; if its not in the manual, you just might be the one whos put in the hot seat to fix a problem! Make sure that known problems are listed with solutions and work−arounds! Following is a categorized list of information that should be provided. Support requirements Availability of application (when it should be available for users as opposed to, say nightly maintenance) Software versions and release Levels (for example, which versions of the software work together on what hardware)when you use open−source software, you need to know from where you got it and where to get it again Installing open−source software (for example, will you be using RPM?) Help desk support and problem management (who to call with when a given problem occurs) Dial−up access for after hours or off−site support Network support requirements and information for network support persons

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How to monitor the vital signs of the systemerror log files, CPU usage, disk usage, disk performance, memory and paging performance; Linux system monitoring tips should be included Linux system configuration requirements Heres a short list of items that are often overlooked because youve started development on an existing system. Desktop environment; Window manager; startup and shutdown; network interface and TCP/IP configuration; assigning users; group assignments; default umask; security and passwords (aging, and so on); programs including execute permissions; backup device configuration (all device configurations); OS kernel parameters Linux backup and recovery procedures Backup and recovery is seen as something to be done later. Usually, later is too late! Picture yourself explaining to the project sponsor why the strategic vision has to be put on hold for a while so that you can put the pieces back together. You should back up system files, user files (maybe even home directories), and the application files. You must determine how often each needs to be backed up. Write this down and put it into the documentation for the system. Send it to the system administrators. Then secure the backups tapes (dont throw them into a box in your desk). You need to be able to get to them quickly. You have only done half of the job. Now, write a recovery procedure and practice it. Many organizations have found to their dismay that their backups are actually blank! Application installation and maintenance The procedures for installing and maintaining the application and/or system are the second most important project deliverable (the first being the system). You must be detailed and comprehensive. Rewrite this document until it is flawless. It helps to have someone who is a capable writer. Make sure you address every step from obtaining the software, confirming the configuration of the hardware, compatibility of other required software, if and how to maintain the software, identifying compatibility problems, and so on. Linux RDBMS installation and management Most of this is available from the open−source supplier (thankfully!). However, you may find yourself augmenting this documentation to fill in the gaps, and pulling together the tools needed for efficient management. For many of the open−source products there is a lack of DBMS management utilities, backup and recovery tools, and monitoring tools that are common with proprietary Linux databases.

From Project Plan to Tables
As the previous section demonstrates, designing and managing a database project is a complex task that involves a considerable range of skills. This section focuses on a key part of part the database project: designing the database. This is the most important single task in a database project, for these reasons: • The databases design controls the rest of your work. A database that is soundly designed will make the rest of your tasks easier, if only because you will not have to work around flaws or inconsistencies in the database.

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• If you intend to use your database for years, you probably will have to update itboth to fix bugs and to add new features. A soundly designed database is robust: it withstands change more easily than one that contains dead ends and contradictions. • Furthermore, a well−designed database is, by itself, the best way to explain your ideas to the people who will maintain the database after you have moved on to other projects. The design of your databaseboth the structure of each table and the interactions among tablesdescribes how you view the real−world entity that your database reflects. The literature on the relational database offers any number of methods for translating entities and events into tables. Some of these are quite elaborate. In our experience, however, a designer can achieve good results by applying a few common−sense principlesand by tempering those principles with art and with experience. The rest of this section discusses the principles; the remainder of the chapter presents you with some examples that walk you through the designing of two example databases.

What does it mean to design a database?
Before we discuss what it means to design a database, lets quickly review just what a database is. • A database is an orderly body of data and the software that maintains it. In the relational model for databases, which we use as our principal way of thinking about databases, a database is composed of relations. • A relation consists of one or more attributes, each of which holds data drawn from a single domain of data. • A domain describes one aspect of an entity or event in the real world. • The attributes that comprise a relation are related to each other, so that together they portray an entity or event in the real world. If a relation is a mosaic that portrays an entity or event, then each of its attributes is a tile in the mosaic. • Relations can be joined to each other through foreign keys. A foreign key is a combination of one or more attributes that are present in two or more relations. These shared attributes join relations together, just as a set of characters that appear in more than one novel join the novels together into a single work. • Through foreign keys, a group of relations can be linked together to form a whole that models a complex, real−world systemthat is, they form a database. If one relation is a mosaic that portrays an entity or event, a database is a series of such portraits, when joined together, portray an entire system of entities. To use another simile, the craft of the database designer is like that of the mechanical engineer. An individual relation is like a gear or bolt that is designed to perform a simple task; and a database is like a machine that assembles many gears and bolts into a whole that performs a complex task. The engineer must design each part so that it is simple, efficient, and easily understood, yet it dovetails with its neighboring parts. The engineer must design the whole so that parts work together efficiently, with no extraneous parts and with all parts easily accessible so that the machine can be repaired easily. The art of the engineerand of the database designerlies in this balancing of the requirements of the whole and of the parts. As the above description illustrates, designing a database has two aspects: • Designing each relation so that it fully yet efficiently portrays the real−world entity or event you have in mind. • Designing the system of relations and how they join, so that together they portray the real−world 133

system that your database models. Of course, most databases are not so elevated; most are simple and straightforward. But as the examples that come later in this chapter show, even a simple database requires thought if you want to do it well.

The steps of designing a database
The following steps describe how we design a database. Our approach is empirical rather than theoretical; however, each step builds directly upon the theory we presented in Chapter 2. Step 1: Articulate the problem The first step in designing a database is to articulate the problem, and to write a requirements document. This is the most important task that you will undertake as a database designer. A well−analyzed project probably can withstand a badly designed database; but the best database design in the world must fail if the analysis that underlies it is faulty. Step 2: Define the information you need After you have articulated the problem, the next step is to ask, What information do I need to solve this problem? In this step, you must name the entities that you must model to solve the problem. In the literature on databases, this process often is called defining the problem space. We prefer to think of it as naming the objects that reside within the problem space. Consider, for example, a system to catalogue your comic book collection. Your requirements document is very simple: Record all information for identifying the comic books in my collection. To solve this problem, you must store information about the following entities: • Each comic book publisher; for example, DC or Marvel. • Each title of which you have an issue; for example, Green Lantern or Fantastic Four. • Each issue of a comic book that you possess; for example, Fantastic Four, December 1966. • Each person who worked on an issue you possess; for example, Gil Kane, Jack Kirby, Steve Ditko, or Stan Lee. These are the entities that you will model in your database. These entities, and how they relate to each other, define how you will think about your database. The rest of your work is to describe these entities and how they fit together. Step 3: Decompose the entities After the entities that will comprise the database are identified, we must decompose each entity into the data elements that define it. (In the literature of databases, the term decompose does not mean to rot; rather, it means to disassemble a composition into its constituent parts.) For example, in our comic book example, one of the identified entities is a comic book title. To identify a title, we need to record the following the data elements: • The publisher • The titles name • The month and year the title began publication 134

We could record other information about a title; for example, whether it is published monthly or bimonthly. However, the elements we listed here are sufficient to solve the problem we articulated in phase 1, which is to catalogue our personal comic book collection. The problem statement will, in fact, guide us in choosing the data elements we wish to gather and store. For example, suppose that one of the entities in our database is person. For a database that catalogues our comic book collection, it is sufficient to record the persons name. We may also wish to record the persons specialty (writer, editor, penciller, inker, or whatever), but not much else is needed. However, for a database that records information about people who have cancer, we will need to record many additional data elements: • Identifying information, such as name, address, telephone number, and e−mail address. • Demographic information, such as date of birth and sex. • Biographical information, such as the industry in which the person works; the persons use of alcohol, tobacco, and recreational drugs; and the persons hormonal and reproductive histories. As you can see, the definition of an entity is dictated by the problem that our database is attempting to solve. Our ability to decompose entities will depend, in turn, in how much we know about the problem area we are dealing with. If you already know the problem domain with which this database deals, then this phase may require just some reflection on your part. If you do not know the problem domainor if the problem domain is complex, as in our cancer exampleyou must research the topic and consult with experts to ensure that you have decomposed the entities properly. Step 4: Design the tables After we have defined the entities that we are modeling and have written down the data elements that we must record to describe each entity sufficiently, we must translate these entities into tables. It is in this phase that the craft of the database designer shines brightest. From this point forward, we speak of tables instead of relations because we are moving from theory into the real world of code that we must actually implement. To begin, each of your designs must state the following for each table: • The attributes (columns) within the table. • The tables primary key. • The tables foreign keys, should it have any. • The indices that we build for the table, if any. You also have to state each columns data type; for example, whether it is an integer or a string, and if it is a string, how long it must be. If we have done our work well in the first three phases of this task, designing the tables is straightforwardmost of the entities that we defined in phase 2 will translate into one table; and each tables columns will be those defined in phase 3. However, some entities do not require their own table; and some do require more than one table.
Rules for translation

So, what are the rules by which we should translate entities into tables? There are two: Our first rule is this: The columns in a table must be existentially related to each other. Please pardon our use of the adverb existentially, but that word does express best the fact that the columns must be essential to the 135

entity we are modeling, and not peripheral to it. For example, if we are writing a database for an automobile dealership, we will want to record the fact that a given person owns a given model and make of automobile. To an auto dealer, the kind of car a person drives is an essential part of his definition of a personto the auto dealer, car is existentially related to what a person is. However, not even an auto dealer will want to record in the definition of person how many cylinders the car has. The number of cylinders is existentially related to the car, not to the person, and therefore should be put into the table with which we describe cars, not into the table with which we describe persons. The person table will have a foreign key that points to the kind of car the person drives. Our second rule is: avoid redundancy. This refers to redundancy of columns, as well as to redundancy of entities within tables. If possible, each entity should appear once and only once within the database. If the table requires multiple iterations of one or more columns, that column probably describes an entity on their own and it should be broken out into its own table. Likewise, if our design requires that an entity be described in more than one row, we probably should break that entitys columns into a table of their own. For example, suppose that your database must record information about a person, including a persons address. You can either move the address columns into a separate table, or you can add them to the table that holds the other data that describe a person. If we only want to record the persons current address, and dont care about any other address at which the person has lived, then it makes sense to add the address columns to the person table. However, there are two circumstances in which we should break the address into its own table: • A person has lived at more than one address. We may be interested in storing all of the persons addresses. For example, an epidemiologist may wish to see whether a person has lived near a uranium mine or a high−tension power line. We could create separate columns for each addressfor example, a column named address1, a second column named address2, and so on through the number of addresses we wished to store. However, this is wasteful and clumsyredundant, in other words. To store all of the addresses at which a person has lived, we should move the address columns into their own table. • More than one person probably lives at an address. We can add the same address again and again to the person table of each person who lives at that address; but this, too, is redundant. This is not as gross an example of redundancy as having multiple address columns within the person table, but it is a redundancy nonetheless. If it is likely that more than one person in our database will live at the same address, and this fact interests us, then we should break addresses into their own table.
Methods of joining tables

The example of person and address raises the question of how tables are joined to each other. As we noted in Chapter 2, tables are joined through a foreign key: one table holds a column whose value points to one or more tuples in another relation. Tables can be joined in any of three manners: • One−to−OneHere, a row in one table has one and only one counterpart in the other table. For example, if each person had one and only one address, this would be a one−to−one join. We would join the two tables either by putting a foreign key in the person table that points to the address table, or vice versaor simply move the address columns into the person table, as we had originally planned. • One−to−ManyHere, each record in one of the tables can point to many records in the other table. For example, in our person−address example, one person can have many addresses, or many persons can have one address. If one person can have multiple addresses, we would put into the address table a foreign key that points to the person table; thus, multiple records in the address table could point to the same record in person. If one address can be held by multiple persons, then we would put into the 136

person table a foreign key that points to the address table; thus, multiple records in the person table can point to the same record in person. • Many−to−ManyHere, each record in each table can point to many records in the other table. In our person/address example, a many−to−many join occurs when each person can have many addresses and many persons can hold each address. In this situation, putting a foreign key into the person table or the address table will not work: as each person can hold multiple addresses, and an address can be held by multiple persons, each table would need multiple foreign keysone for each address or person being pointed to. This, of course, is highly redundant, and therefore will not do. To build a many−to−many join, you must insert a third table into the database to hold the keys of the rows being joined. In our example of the person and address tables, we would create a third table that consists of two columns: one holds a foreign key that references the person table, and the other a foreign key that references the address table. Each record in this third table links one person with one address; thus, we can link a person to as many addressesand an address to as many personsas we like. Such utility tables within a relational database are quite useful. It is not a good idea to let them proliferate, but they can make for a cleaner design by helping you to avoid polluting a table with multiple instances of the same column.
Normal form and normalization

So far so good: we want to make each table hold only the columns that are existentially part of the entity it is modeling; and we want to avoid redundancy within the database. The question now arises: Is there a method by which we can analyze our tables to avoid redundancy? The answer is yes, thanks again to the work of E. F. Codd. Codd proposed a process called normalization, by which a database is translated into normal form. The literature recognizes many levels of normal form; the higher the level, the closer the database approaches to the pure relational form. However, four levels of normalization are used most commonly: • First normal form • Second normal form • Third normal form • Boyce−Codd normal form (BCNF) There are other levels beyond this, but the four mentioned here are quite sufficient for most work. In the following sections, we introduce each normal form briefly, and then discuss how we use normalization to design tables. But before we do that, we must introduce one last notion: that of functional dependency.
Functional dependency

The idea of a normalized database depends on the idea of functional dependency. This is a simple concept: in brief, it states that the value of one column depends upon the value of another. For example, consider an automobile manufacturer, Acme Motors. Acme builds two varieties of car: one has six cylinders, and one has four. Each make of car that Acme manufactures comes in one of these two varieties; for example, the Banshee and Thor have six cylinders, whereas the Zeus, Odin, and Loki have four. If we build a database that describes Acmes products, the column that gives the number of cylinders functionally depends upon the column that gives the cars make, because the make determines the number of cylinders a car has, not vice versa. Functional dependency is another way of expressing our existential rule for database design. After all, true functional dependency reflects the nature of the entity or event that the table reflects: every functional 137

dependency in our database should, in some way, reflect a functional dependency in the real world. Much of the process of normalizationand much of what goes under the term normal formis simply the process of identifying functional dependencies, and organizing tables around them. Now we ready to introduce the types of normal form.
First normal form

First normal form states that every column contains a scalar. A scalar is an atomic data typethat is, a data type that cannot be reduced mathematically to a collection of simpler data types. Thus, to achieve first normal form, a column cannot hold a structure or another table. As you will recall from Chapter 2, this is part of the definition of a relational database. To be called relational, a database must adhere to first normal form.
Second normal form

For a table to conform to second normal form, each of its columns that is not part the primary key must depend irreducibly upon the key. A table will not conform to second normal form if its primary key consists of more than one column, and one or more of its non−key columns depend upon part of the primary key, but not all of it. For example, consider a table that describes telephone numbers. It consists of three columns: area code, telephone number, and the town in which the telephone number is located. Some sample telephone numbers are:
AreaCode Number Town 312 3825968 Chicago 312 3287448 Chicago

The primary key of this table is the area code plus the telephone number. As it happens, however, the name of the town does not irreducibly depend upon the primary keyan area code always lies within a town (as is the case with area code 312 and Chicago) or a town lies entirely within a given area code. Thus, the town depends not upon the entire primary key, but on only part of itthat is, the area code. To put this table into second normal form, we must break it into two tables:
AreaCode Number 312 3825968 312 3287448

and:
AreaCode Town 312 Chicago

As you can see, this reduction to second normal form eliminates the redundant appearance of Chicago within the table. It also brings the table into line with our common−sense rule of avoiding redundancy in a database.

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The simple definition of BCNF subsumes first. NULL. it must adhere to first and second normal form. NULL.Third normal form
For a table to conform to third normal form. NULL. Earlier. The process of normalization is a pencil−and−paper task by which we can turn a bag of columns into a neatly dovetailed set of tables. Relational theorists have proven that a database can always be transformed into third normal form without losing information (although this proof is beyond the scope of this book. This gives us the following table:
CREATE TABLE book ( isbn title authors price publicationYear
CHAR(20) VARCHAR(255) VARCHAR(255) INTEGER INTEGER
NOT NOT NOT NOT NOT
NULL. in which the person table also mentioned the make and model of the automobile that the person currently owns. Adding cylinders to a person table would also violate third normal form. a table cannot contain a key that controls some of the columns in that table. second. we mentioned an example of an auto−dealership database. our database must describe books. A table adheres to BCNF if and only if every column within the table functionally depends only upon the tables primary key. except for the column (or columns) that comprise a primary key.
139
. We will make the ISBN number the tables primary key because that is a simple number that is assigned to one and only one book. BCNF is easier to demonstrate than it is to explain. every column must be independent from every other column. we would have a nonperson column grafted onto a table that was describing a person. but upon the car column. but we rejected the idea because it would violate our rule of existential integritythat is. we can gauge whether a table truly adheres to the relational model. In other words. With this single rule. furthermore. so we give an example momentarily.)
Boyce−Codd normal form
The Boyce−Codd normal form (BCNF) is a more robust statement of the third normal form. and a description of a book can include these columns: • Title • Authors • Price • ISBN number • Year of publication • Publisher • Publishers address Our initial design includes all of these columns within a single table. we now have a simple rule by which we can gauge the relationality of the tables in our database. and third normal forms. Among other things. NULL. For example. Our database would be sounder if we broke the car and cylinder columns into a separate car table. but not all of them. because the cylinders column would depend not upon the tables primary key. We considered whether to add the number of cylinders of the cars engine to that databases person table. lets suppose that we are designing a database that will hold a bookstores inventory.
Normalization
As you can see.

the publishers address would change. rather. price INTEGER NOT NULL. isbn). However. PRIMARY KEY (isbn) )
However. publicationYear INTEGER NOT NULL. PRIMARY KEY (authorName. it depends upon the name of the publisher. We could create separate columns within book table for each possible authorcalled. the authors name is all the information we need: we do not want to cross the thick black line weve drawn around this project unless we absolutely must. This violates BCNF. which violates the rule of avoiding redundancy. publisherAddress VARCHAR(255) NOT NULL. we see that each book can have an indefinite number of authorsmost have one or two. title VARCHAR(255) NOT NULL. we see that one columnpublishers addressdoes not depend upon the ISBN number directly. 140
. FOREIGN KEY isbn REFERENCES book )
If we were a publisher and needed more information about an author than just the authors name. publicationYear INTEGER NOT NULL. PRIMARY KEY (isbn) FOREIGN KEY (publisher.publisherName) ) CREATE TABLE publisher ( publisherName VARCHAR(128) NOT NULL. PRIMARY KEY (publisher_name) ) CREATE TABLE authorBook ( authorName VARCHAR(255) NOT NULL. without affecting the other columns in the table. when we apply the rule of BCNF. but some can have as many as six or more. and join it to table author−book through a foreign key. we would create an additional table to hold that information. If the publisher were to move. price INTEGER NOT NULL. authors VARCHAR(255 NOT NULL. when we look again at table book. which joins authors with books.publisherName) ) CREATE TABLE publisher ( publisherName VARCHAR(128) NOT NULL. so good. Therefore. thus. we will divide authors into their own table. each book can have multiple authors. author2. and each author can have written multiple books. PRIMARY KEY (isbn) FOREIGN KEY (publisher. PRIMARY KEY (publisher_name) )
So far. because we are writing a database for a bookstore rather than for a publisher. However. author1. and so onbut that would be adding redundant columns to this table.publisherName VARCHAR(128) NOT NULL. The revised design now appears as follows:
CREATE TABLE book ( isbn CHAR(20) NOT NULL. say. title VARCHAR(255) NOT NULL. This satisfies the many−to−many relationship between authors and booksthat is. we will divide columns publisher_name and publisher_address into their own tablepublisherthat we join to table book table through a foreign key. Our revised design now appears as follows:
CREATE TABLE book ( isbn CHAR(20) NOT NULL. isbn CHAR(20) NOT NULL. publisherAddress VARCHAR(255) NOT NULL. publisherAddress VARCHAR(255) NOT NULL.

we write down the databases domain−integrity rules. you often have to revise your database while it is in day−to−day operation. It is not difficult to be either simple or straightforwardthe trick is to be both at the same time. Here. at last. we implement them in software. 1982). it is easy to dobut difficult to do well. experience is your best guide. this design may seem to be more convoluted than our initial design. when we introduced SQL. However. Step 5: Write domain−integrity rules As the last step in designing a database. The examples in the following chapter sections.
Building a Simple Database: The Baseball Example
Now. We begin with a simple example: a small database to hold the scores of baseball games. as you get further into this book. and you will work some or all of them into the software with which you manage your database.At first glance. you will have to choose whether to perform a task with a few simple tables. you will discover more and more rules that govern domain integrity. if we design a table that holds an address. The difficulty makes it challenging. and you will have an idea of some of the problems that can afflict a database manager. ways to improve the database appear continually. For example. Much of the art of database design comes in the balancing of simplicity and straightforwardness: often. or one more complex table. A well−designed machine works efficiently: no part is extraneous.
The art of database design
In his book The Mythical Man−Month (Addison−Wesley. Like most truly creative acts. but here we discuss how we came to design the database in the way that we did. A normalized relational database withstands change better than one that is not normalized. we may wish to write a domain−integrity rule that states that no address can have the ZIP code 00000 because there is no such ZIP code. however. The effort you spend in designing your relations well will pay great dividends over the life of the database. Unlike a machine. No database project is ever really ended. We already used this database in Chapter 3. every part works well with all of the others. the creativity makes it fun. These rules check whether the data being written into the database are consistent with the nature of the domain of which our database is a model. 141
. Designing a database is a creative act. It is also an ongoing phase: as you work with your database. which simply dumped all of the columns into a single table. no address can have it. [T]hat system is best in which one can specify things with the most simplicity and straightforwardness. each part is as simple as possible. thus. Think of your database as being a machine for the storage and manipulation of data. These rules are useful because they will help us prevent nonsense from being written into the database. Frederick Brooks wrote. This phase is the last in the process of database design. Think of rebuilding an airplane while it is in flight. Domain−integrity rules are not part of the database per se. The following examples suggest the difficulty and the creativity of database design. you will see that a normalized relational database is both easier to program and easier to maintain than one that is not normalized. we use the theory that we have presented to design a database. show some instances when we had to select one approach or the other. Rather.

we must not only name the two teams that are playing. In baseball. What information do we need to solve this problem? In this example. we must also note which team is the home team. • The teams home city or state. we want to build a system that records information about baseball games. Our problem statement draws a very thick. too. We are not interested in modeling a baseball game in all of its complexity: runs. However. very black line around this project. in particular the city in which a team plays and the stadium in which it plays. • Because teams sometimes play double headers (that is. we also must record whether the game was the first or second game played on a given day. we need to record information about two entities: • The game itself. Still. errors. A games importance depends upon whether it is played during the regular season or during the playoffs.Step 1: Articulate the problem
In this example. hits. • The teams that played the game. by counting the number of games that each team has won. The task we set ourselves is very simple: Record the score of each official game played by two major league teams. is peripheral to our original problem statement. the problem−statement does not require that we gather detailed information about these entities. • The day the game was played. We discuss this in step 4. This last point. 142
. our next step is to ask. Note the words official (which excludes exhibition games and spring training) and major league (which excludes amateurs and minor leagues). however. • The number of runs that each team scored. Note. fielding chances. Each game consists of: • The names of the teams that are playing the game. we can add a great deal of functionality to our little database by adding this one column. This information is important.
Step 2: Define the information we need
Now that we have articulated the problem. attach themselves to the project. we will be able to compute which team wins its division during the regular season. so our database will not describe them in detail. they play two games on the same day). that we are just recording the score of the gameno other statistic. in truth. the names of the winning and losing pitchersnone of this interests us at this time. For each team. and their accumulated mass eventually drags the project into the mud. We also want to record the league and the division in which a team plays. • The name of the stadium in which the team plays. we must be careful to avoid creeping feature−itisa fatal disorder that occurs when attractive little features creep into our minds. one team is the home team and the other is the visiting team. earned runs. so we need some way to determine whether a game is a regular season game or a playoff game. we need to record information by which it can be identified: • The name of the team. so we will add it. as the rules of baseball give the home team a distinct advantage. Thus. The database will also name other entities.
Step 3: Decompose the entities
Our next step is to decompose each of these entities into its constituent elements.

the number of other professional sports teams that it supports. for example. its data changes infrequentlyand the names of the teams are well known. for example. At this point. our database comprises two entities: baseball teams. and the games they play. we do not model these entities within tables of their own because we are only interested in their names.Step 4: Design the tables
Now that we have decomposed each entity into the data elements that comprise it. If other columns interested us about the citysay. However. Cubs or Brewers. for example. our next step is to design tables to hold those elements. Column stadium names the stadium in which the team plays when it is at home. For each column. or its population. Finally." Minor leagues. It is unusual to use a name as a primary key because of the practical consideration that keys often are values that are entered into the system by users. But we are not interested in those columns.
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. that is. Teams Table team describes a baseball team:
CREATE TABLE team ( team_name CHAR(15) NOT NULL. Central. so in this instance. As we noted in the previous subsection. PRIMARY KEY (team_name) ). column division names the league division that the team is in. like any good engineer or scientist. and users often mistype or misspell strings. league CHAR(1) NOT NULL. likes to wield Occams Razor. stadium CHAR(30) NOT NULL. This table has no foreign keys. it will be "National" or "American. We will also give each tables keys. The following subsections name each table and its columns. it is acceptable to use a name as a primary key. However. city CHAR(15) NOT NULL. Adding these extraneous columns would smudge the thick black line we have drawn around the project. division CHAR(1) NOT NULL. and does not multiply entities unnecessarily. or the state in which it is locatedthen it would make sense to divide city into its own table. The same applies to stadium as well as to league and division. The good database designer. for example. the International League or the Pacific Coast League. We will define one table for each.
Column team_name names the team in question. or West. It has one primary key. but could easily be inserted into this column. Wrigley Field. Column city names the home city or state of the team. In this instance. are beyond the scope of our databases problem statement. the table team is a static tablethat is. so it makes no sense to put city into its own table. which are also entities in themselves. the name of the team. We mentioned earlier that both city and stadium are entities unto themselves. East. relational theory comes into play. Column league names the league in which the team plays. we will note whether it is forbidden to hold NULL. Chicago or California.

Indices should be built for all of the columns with which users will be performing look−upsbut no more than that.Games Table game gives the score of each game. the number of the game. if we did not make that distinction. after that you must use your best judgment. and in part because the rules of baseball give the home team a distinct advantage. game_number SMALLINT NOT NULL. The winning team is the team that has scored more runs. Each is a foreign key that joins this table to table team. you would not need a relational database. game_date CHAR(10) NOT NULL. game(home_team). FOREIGN KEY (home_team) REFERENCES team ). PRIMARY KEY (home_team. As a rule of thumb. We record the names of the visiting and home teams separately. Because teams occasionally play two games on the same day. game(home_team. so you dont have to get your suite of indexes exactly right before you begin. we will build the following indices:
CREATE UNIQUE INDEX index1 ON CREATE INDEX index2 ON CREATE INDEX index3 ON CREATE UNIQUE INDEX index4 ON team(name). it is difficult to predict just what columns will be used in look−ups. game_date. you should give every key an index. column game_number gives the number of the gameeither one or two. We need the number of the game so that we can distinguish among games played by the same teams on the same day. We could break the teams into a separate table. game_number).) Fortunately. Another way to solve this problem is to record the time that each game started. because each team fulfills a very different role in the game. we could not build a primary key for this table. Indices As we noted above. The primary key combines the date. game_date. in part because we want to be able to see where the game was played. For this database. (If you could know ahead of time just what queries users would want to make on a database. Column game_date gives the date the game was played.
Columns home_team and visiting_team names the teams that play the game. as follows:
CREATE TABLE game ( home_team CHAR(15) NOT NULL. visiting_team CHAR(15) NOT NULL. because a team never plays two games simultaneously. game(visiting_team). home_team_runs SMALLINT NOT NULL. designing a set of indices must balance speed of lookup against cost of building the index and the disk space it consumes. game_number)
144
. visiting_team_runs SMALLINT NOT NULL. but we would still have to have two foreign keys to that tableone for home team and one for visitingso doing so doesnt gain us anything. This may seem to violate our rule that forbids redundancy. Before people begin to use a database. Columns home_team_runs and visiting_team_runs give the number of runs scored by each team. and home team. but it does not. you can build and drop indices without affecting the structure of the database.

A user can borrow a book for two weeks. but these will give us a good start. and is only used to look up information. our names index1.
Step 1: Articulate the problem
As with our simple example. columns home_team and visiting_team must never be identical. • A team can never have a negative number of runs.CREATE
INDEX index5 ON game(visiting_team. hence.
Step 5: Write domain−integrity rules
Table team is static. It also gives us a method by which we can gauge whether our system is successful: it will be successful if it can tell us who has possession of any book right now. therefore. a column can be used in more than one index. If the user returns it late. game_number)
As you can see. game_date. The names do not have to be descriptive. except that the information be accurate. and then returns them. We do not need any rules for it. we begin by articulating the problem: The library must record who has possession of any given book at any given time. Our task is to design an information system for a multibranch library. Naming an index lets us manipulate it later. This statement tells us what the system must do. and so on. The librarys collection has one or more copies of each book. No doubt we will think of other rules as we gain experience in working with our database. in case we wish to alter or drop it. Table game requires these rules: • A team never plays itself.
145
. each of whom can borrow books from any of the branches. • Teams never play more than two games on a given day. we will walk through the steps of designing a database for this problem. therefore. Again. with the copies being distributed across one or more branches. it lends books to users. so column game_number must always equal one or two. and our databases design will reflect this complexity. therefore. This problem is considerably more complex than the baseball score problem. index2.
Building a More Complex Database: The Library Example
In this section. Our library is a lending librarythat is. columns home_team_runs and visiting_team_runs must never be less than zero. We give each index a name. we design a more extensive database that tackles a real−world problemtracking the books in the collection of a multibranch public library. The library has a body of users. • A baseball game can never end in a tie. columns home_team_runs and visiting_team_runs must never be equal. Each user keeps the books that the user has borrowed for a fixed period of time or less. or even imaginative. the user pays a fine.

and the act of possession. So far. CDs. the Chester A. The above data identify a book title. we want to record the price of book. The next step is to decompose each entity into its constituent elements. plus the number that uniquely identifies a given copy of the title. Arthur branch library may have three copies of the Linux Database Bible. After all. and the action of possessioncan be further divided. each of these entitiesthe possessor. and periodicals. To answer the question of who has possession of a given book at a given time. Our description of a book must flag this fact. the possessor. you can see that it can be identified in the following ways: • By title • By authors names • By publisher • By city and year of publication • By ISBN number In addition. So. a physical bookwe need all of the above information. we need information about the following entities: • What can be possessed (in this case. The possession The possession is something that can be possessedin this case. However. we ask what information we need to solve the problemthat is. we must identify the branch to which the copy belongs. the number of color plates. Finally. a library system can have multiple copies of the same title. Each copy will be owned by a given branch of the library. the books). DVDs. its weight.Step 2: Define the information we need
Now that we have articulated our problem. • Who or what can possess a book at any given time (in this case. to identify an individual volumethat is. and the act of possession involves borrowing items and returning them.
Step 3: Decompose the entities
As we have seen. A book has many featuresits size. our library system needs to manage information about three entities: the possession. a book will have been assigned either or both of the following numbers to a book: • Library of Congress number. well ignore the fact that libraries also handle other materials. This will let us recover its cost should it be lost. How we will do this must await our 146
. For example. and decompose it into its constituent parts. a possessor can be a user or a library. what entities inhabit the problem space. Therefore. the library and its patrons). so good. Hayes branch may have only two. a book. such as videotapes. Some books are not suitable to be borrowed by minors. If you look over the book in your hands. our next step is to take each item of information that we need. For the sake of simplifying our example. • Dewey Decimal System number. and so onbut for our system we are interested just in the information with which the book can be identified. So. • Which possessor possesses each book. However. the possession. whereas the Rutherford B.

we need to decompose each of these separately. but it would be unwise to do so. As we noted earlier. we will include address and telephone number as a convenience to the persons who will use our system.detailing how we will describe each branch of the library. An information system should not only tell us the current state of the entity it models. or it may be marked as lost or stolen. Each branch can be described many ways. as you recall from Chapter 2. we will forget all transactions that involved this book. a person must apply for and receive a library card. So. such as by the name of the architect who designed it. our library consists of a number of different branches. this is necessary to maintain database integrity. Finally. A user is a person who has permission to borrow books at our library. For this reason. To borrow books. the user doesnt return a book that the user has borrowed. which means that. we need to record the copys status. we must also remove all records that reference it. in effect. The possessor A library or a user can possess a book. However. if we remove a record that describes a book. After a user possesses a card. then. if we remove a given record from our database. needs information with which it can identify a person. Thus. However. we must also remove the records that reference it. may have become ineligiblethe user may have moved away. The user. or died. say. some study and reflection shows that a branch library can best be identified in the following ways: • Its name • Its address • Its telephone number Strictly speaking. we want to mark the status of books that are no longer in our library. We could purge all of this information from our system. We could mark a copy as being unavailable by simply removing its record from the database. Some thought and study show that our library system needs to record the following information by which the library can identify and contact a user: • Name • Address • Telephone number • Social Security number • Date of birth • Users status We need to record date of birth in order to determine how old the user isour library restricts some materials from access by minors. Our library system. it should also be an archive that we can explore to discover the state of our entity in times past. or lost his or her privileges (perhaps the user borrowed some books that the user never returned). It also needs the information with which it can contact a personin case. a user can 147
. so that our system can remember the transactions that involve them. The status datum indicates whether a user is allowed to borrow books. A copy may be discarded. all we need to identify a branch library is its name (assuming that the name is unique within the library system). however. and so discover how the entity is changing over time. after all.

we will want the system to disallow borrowing by anyone who possesses the first card (after all. or the library may have withdrawn it from circulationfor example. As we noted earlier. For example. The user can also return a book to any branch. • The date the card is issued. because a user can have many library cards during his or her lifetime. • The status of the card. Our library system will have to record the following information about a library card: • The identification number of the card. in this case. the status datum indicates whether a card can be used. Furthermore. • The fact that a given card is possessed by a given user. the street name. or it will be in a library branch. the user may lose his or her card and be issued a replacement. A card may have been reported as being lost or stolen. for our library system that would be overkill. we mentioned that we need to record the address and the telephone number for each. we could decompose the street address into the number.). A telephone number can be decomposed into these elements: • Area code • Number Again. the card may have been stolen) but still permit borrowing with the replacement card. the book must be 148
. The act of possession Someone or something will always possess a book: either a user will have borrowed it. a user can borrow a book from any branch of the library. it may have become worn out and the library may have issued a replacement. we assume that all telephone numbers are within the United States. We will do so because our system will be able use some of the information that is embedded within each. In our description of library branches and users. We record the date the card is issued so that we can retire cards after a defined number of years. Both address and telephone number can be decomposed further. 1234 N. Again. Some of the address elements can be decomposed further. An address can be decomposed into these elements: • Street address • Apartment or unit number • City • State • ZIP code We assume that all addresses are within the United States. Main St. The only way to meet this criterion is to have the library apply a unique number to each card.borrow a book from any of the librarys branches. We mention the library card apart from the user. however. If a book is returned to a branch other than the branch that owns that book. and the direction (for example.

Step 4: Design the tables
Our next step is to design tables to hold those elements. we need the following information: • The user paying the fine. we need the following information: • The book being transferred. To describe a borrowing event. • The date he paid the fine. the physical books). Thus. • The user who borrowed the book.transferred to its home branch before it can be borrowed again. when a user returns it. • The date it was borrowed. to define who has a book at any given time. we need the following information: • The book being returned. One last event must be described: a fine. We do not need to record who returned the book. and when a book is transferred from one branch to another. 149
. • The amount of the fine. • The branch from which it was transferred. We can assume that if a book has not been borrowed or is not being transferred from one branch to another. When a user pays a fine. and to do so. a user must pay a fine for every day that the user keeps a book longer than the normally allowed borrowing period. A book can change hands in three different ways: when a user borrows it. possession consists of two entities: the book titles that our library houses. As we noted earlier. • The branch to which it was returned. The possession As we noted above. we need the following information: • The book being borrowed. We do not record where the book was borrowed from. We assume that a book is always transferred to its home branch. we must record the fact. that it is residing in its home branch. we must record when the book changes hands. • The date it was transferred. To describe a transfer event. The following discusses each of these events. and the copies of each title (that is. because we already know who borrowed it. • The date it was returned. To describe a return event. because we assume that a book is always borrowed from its home branch.

branch_code CHAR(5) NOT NULL. publisher VARCHAR(128) NULL. Minors cannot borrow adult books. This table has one primary key. Column branch_name gives the name of the branch that "owns" this copy. the books ISBN number. year. loc_number. and Dewey Decimal number. adult_flag CHAR(1) NULL. Columns title and author give the title and author of the book. Column copy_number gives the number of this copy of the book. FOREIGN KEY (branch_code) REFERENCES branch ). Other columns can vary in length. loc_number CHAR(20) NULL. Table copy describes a copy of a book:
CREATE TABLE copy ( title_id_number INTEGER NOT NULL. Columns isbn. copy_number INTEGER NOT NULL. Column adult_flag flags whether this an adult title. column id_number. after estimating what the maximum amount of text each would hold. We permit these to be NULL because they may not be known. such as loc or adult_flag. we permit these fields to be set to NULL. PRIMARY KEY (title_id_number. price INTEGER NULL. year INTEGER NULL. Some columns.
150
. For this reason.
AUTO_INCREMENT. and they are not essential to identifying a title. respectively. city. It does not reference any other tables.
Column title_id_number gives the key of the title. isbn CHAR(20) NULL. ). and price give information about the books publication. PRIMARY KEY (title_id_number). Library of Congress number. and ddn_number give. author VARCHAR(128) NOT NULL. so it has no foreign keys. FOREIGN KEY (title_id_number) REFERENCES title. copy_number). ddn_number CHAR(20) NULL. Most books will not have all three numbers set. these we set to CHAR. consist of a fixed number of characters. The keyword AUTO_INCREMENT is used by MySQL to automatically assign a unique value in this column whenever a record is inserted into the database. we made our best guess as to how much storage each column would require. city VARCHAR(64) NULL. With regard to the data type we assigned to each column. Columns publisher. as set in table title. older books will not have an ISBN number. these we set to type VARCHAR.
Column id_number gives a unique identifier for the title.Table title describes a book title:
CREATE TABLE title ( title_id_number INTEGER NOT NULL title VARCHAR(255) NOT NULL.

Column branch_code is the primary key. therefore. As there are only a few branches. ). Columns area_code and phone give the telephone number of the branch. For that reason. Most branches have a number of telephone extensions.
NULL. NULL. NOT NULL. NOT NULL. whereas the other describes the library card with which a user can borrow books. and so onwould be more trouble than it was worth. Table branch describes a branch of our library:
CREATE TABLE branch ( branch_code CHAR(5) NOT branch_name VARCHAR(64) NOT street VARCHAR(64) NOT city VARCHAR(32) NOT state CHAR(2) NOT zip CHAR(5) NOT area_code CHAR(3) NOT phone CHAR(7) NOT PRIMARY KEY (branch_code). that is. A user is described in two tables: one describes the user himself. we discussed the fact that an address is an entity unto itself and could be broken out into its own table.
CREATE TABLE user ( first_name VARCHAR(32) middle_init CHAR(1) last_name VARCHAR(32) birthdate DATE
NOT NULL. Because this table references no other tables.The number of the books title and the copy number must together identify the book uniquely.
Column branch_code gives a brief mnemonic code that uniquely identifies the branch library. The possessor Two entities can possess a book: a user and a library branch. Columns city. a column can be used in more than one tabletitle_id_number is both a foreign key and part of this tables primary key. However. there is a one−to−one relationship between address and the entity that is at that address (user or branch). it has no foreign keys. NULL. this is not difficult to do. we simply embedded the branchs address within its table. NULL. but all have only one main number. NULL. NULL. For that reason. NULL. Columns title_id_number and branch_name are declared to be foreign keys. someone who has permission to borrow books. we decided that breaking addresses into their own tableand setting up the mechanism for relating them. street. NULL NULL. This is a primary key. Column name gives the branchs name. Each branch must be named uniquely. and zip give the branchs address. and is the field that other tables use for their foreign keys to join themselves to this table. The same holds true for telephone number.
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. A library branch is described in one table. When we decomposed the concept of a branch in the previous section. we made this pair of columns the tables primary key. policing the integrity between the two tables. Table user describes a user of the library. because each references a column in another table. state. As you can see.

so it has no foreign keys. after all.ssn CHAR(9) street VARCHAR(32) unit VARCHAR(32) city VARCHAR(32) state CHAR(2) zip CHAR(5) area_code CHAR(3) phone CHAR(7) status CHAR(1) PRIMARY KEY (ssn) ). and zip give the users addressrespectively. the user may have died. state. Column birthdate gives the date the user was born. and last_name respectively give the users first name. because some people do not have a middle name. ssn CHAR(9) NOT NULL. A consistent scheme for naming columns will make it much easier to code your database and to interrogate it. middle initial. A user can become inactive for any number of reasons: the user may have moved away from our community. FOREIGN KEY (ssn) REFERENCES user ). Although it is not required. date_issued DATE NOT NULL. The "middleware" that we write for this application will cover setting and unsetting a users status. tables user and branch each have a column that gives ZIP code. at least). PRIMARY KEY (card_id_number).
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. or the user may have unpaid fines or have a book that is long overdue. we named that column zip. and are lost or stolen. Column ssn gives the users Social Security number. NOT NULL. Column unit can be NULL. cards wear out. Our system will use this date to compute whether the user is a minor. Columns street. NOT NULL. status CHAR(1) NOT NULL. are run through the wash. Columns area_code and phone give the users telephone number. and ZIP code. NULL.
NOT NULL. Column ssn is this tables only primary key. NOT NULL. state. Column status flags the users statuswhether the user is active or inactive. the street number and name. and to ensure that each user has only one card that is active at any given time. middle_init. because some users live in single−family homes that do not have unit numbers.
Columns first_name. For example. As you can see from our address and telephone−number columns. Table card identifies a library card. and a Social Security number is unique to each person (in theory. city. unit or apartment number. This table does not reference any other tables. city. unit. NOT NULL. it is a good rule of thumb to give the same name to columns that hold the same information. NOT NULL. NOT NULL. and in each instance. we have given the same name to every column that holds the same type of information. One user may have held many library cards over the years that the user has patronized our library. We record information about the card apart from information about the user because we want to ensure that bogus cards are not in circulation. NOT NULL. Note that middle_init can be NULL.
CREATE TABLE card ( card_id_number INTEGER NOT NULL AUTO_INCREMENT. We use Social Security number as the primary key because each person in the United States past the age of one year must have a Social Security number. and last name.

They form a foreign key to their namesake fields in table copy. • A book is transferred from one library branch to another. or stolen. Column ssn gives the Social Security number of the user whose card this is. A card can remain in use only for a set period of timesay. five yearsafter which it must be replaced. Even if this were allowed. copy_number) REFERENCES copy ). It initializes the columns card_id_number. copy_number INTEGER NOT NULL. Column date_issued gives the date that this card was issued to this user. Columns borrow_date and return_date give. PRIMARY KEY (card_id_number. respectively. so the database will automatically generate this number for us. Because we use the keyword AUTO_INCREMENT.Column id_number gives a unique number that identifies this card. This column is a foreign key to its namesake column in table card.
Column card_id_number gives the unique identification number of the library card with which the book was borrowed. copy_number. title_id_number. Borrowing a book and returning it are two halves of the same event. Our design assumes that the same person cannot borrow 153
. the dates that the book was borrowed and returned. There are three such acts: • A user borrows a book from a library. When the user borrows a book. so we will use one table to record both:
CREATE TABLE borrow ( card_id_number INTEGER NOT NULL. borrow_date DATE NOT NULL. Columns title_id_number and copy_number identify the book being borrowed. A card that is not active cannot be used to borrow a book. We assume that a user can borrow a book only from the books home library. Note that title_id_number and copy_number do not form a primary key because a given copy of a book will be borrowed many times over the years. return_date DATE NULL. FOREIGN KEY (title_id_number. return_date must allow a NULL value. which together form the tables primary key. copy_number. This column is the foreign key that joins this table to table user. Column status gives the status of the card: whether it is in use. borrow_date). • A user returns a book to a library. If a cards status indicates that it has been lost or stolen. and borrow_date. title_id_number. Act of possession An act of possession occurs whenever a book leaves the possession of one entity (library or user) and enters the possession of another. expired. our system will notify the branchs security person should someone try to borrow a book with that card. FOREIGN KEY (card_id_number) REFERENCES card. title_id_number INTEGER NOT NULL. so we will ignore them. lost. there is no way that we can trace such transfers. the library application creates a record for table borrow. We also assume that a user cannot loan a book to another. because it will be NULL when the book is borrowed and will remain so until the book finally is returned.

send_branch_code. Also. We could record a return event in one table. transfer_date). Column send_branch_code identifies the branch that is surrendering possession of the book. a user can return a book to any branch library. we design our transfer table as follows:
CREATE TABLE transfer ( title_id_number INTEGER NOT NULL. Therefore. receive_branch_code. which is comprised of all the columns in the table. Column receive_branch_code identifies the branch that is receiving possession of the book. a book can be borrowed only from its home branch. These form a foreign key to table copy. FOREIGN KEY (title_id_number. FOREIGN KEY (receive_branch_code) REFERENCES branch ). transfer_date gives the date that the book was transferred. The system then initializes return_date to the date the book was returned. where they are sorted and sent back out to their appropriate branches. When a book is returned to a library other than its home branch. This tells us who has the book right nowor at least tells us who last accepted responsibility for the book. the system looks up every record in the system for which title_id_number and copy_number equals those of the book. copy_number) REFERENCES copy. We assume that the book was sent and received on the same day. If a user wishes to renew his or her borrowing of a book. We do not use card_number to look up the book because books are often returned in book drops or carrels. This means that a book that is being transferred will be moved twice: once from the branch to which it was returned to the central library.
Columns title_id_number and copy_number together identify the volume that is being transferred. Both are foreign keys to table branch. the book must be returned home. Finally. however. however. When the user returns the book. a system 154
. until it arrives back at its home branch. This means that the book must be transferred from one branch to another. copy_number. cash. we prefer to record each time the book changes hands. or medical specimens. As we noted in our analysis section. which (we think) is not too restrictive a rule. and opens a new borrowing for the same user and same copy. Our design simply assumes that whoever received the book last still has possession of it until it is logged as having been received by someone else. Our system will be able to trace the movement of a book through the system. Because we have a well−organized library system. and for which return_date is NULL.the same book more than once on the same day. PRIMARY KEY (title_id_number. This design does not trace the book while it is in the possession of the truck driver who is transporting it. transfer_date DATE NOT NULL. and no card is available. because this procedure may change in the future. FOREIGN KEY (send_branch_code) REFERENCES branch. This table has only one primary key. and once from the central library to its home branch. copy_number INTEGER NOT NULL. receive_branch_code CHAR(5) NOT NULL. a book may have been returned and its return not recorded (the borrower may have snuck the book back into the library to avoid a fine). For valuable objects such as jewelry. so more than one "borrow" event may be open for a given book at a given time. all books that are being returned to their home branches are first returned to the central branch. send_branch_code CHAR(5) NOT NULL. the system simply marks the current borrowing has having been returned.

When a user returns a book. copy_number. but that would be overkill in our library system. Fines One last item of information needs to be described: when a user keeps a book too long. because the user may not pay on the spot. copy_number. Column return_date gives the date that book was returned. These columns form a foreign key that join this table to table copy. and copy_number. title_id_number. plus card_id. the system will compute the users fine and whether the user paid it. PRIMARY KEY (card_id_number. the system will check whether the book is overdue. We do this because we want to be able to trace back the fine to the borrowing event for which the fine was levied. Columns title_id_number and copy_number identify the book that was overdue. return_date) REFERENCES borrow ). We assume that the amount of the fine and the amount paid are the same. will vary from time to time. It also assumes that the same person will not return the same overdue book more than once on the same date. We may wish to add an additional flourishif the user has any unpaid fines. 155
. This column. title_id_number. copy_number) REFERENCES copy. The primary key for this table combines the columns card_id_number. Our fine table looks like this:
CREATE TABLE fine ( card_id_number INTEGER NOT NULL. If it is. Column amount gives the amount of the fine. FOREIGN KEY (card_id_number. Two design considerations should be discussed further. date_levied). and the amount of the fine. amount INTEGER NOT NULL. FOREIGN KEY (card_id_number) REFERENCES card. FOREIGN KEY (title_id_number. return_date DATE NOT NULL. as the librarys policy changes. This is a foreign key that joins this table to table card. title_id_number. and return_date. Column paid_date gives the date upon which the user paid the fine. copy_number. We also use this date to mark when the fine was leviedthe system will levy the fine as soon as the book is recorded as having been returned. paid_date DATE NOT NULL. form a foreign key that joins this table to table borrow.should log every time the object changes hands. When we code this part of our library system. title_id_number. title_id_number INTEGER NOT NULL. the system will not allow the user to borrow books. copy_number INTEGER NOT NULL. the user must pay a fine.
Column card_id_number identifies the library card with which this book was borrowed. This assumes that the same person may keep the same book overdue more than once. The length of time that a user is allowed to keep a book. we must enable administrators to change these values without having to write code or recompile the system. We record the date paid separately from the date the fine was levied.

However. ON branch (branch_code). ON copy (title_id_number. ON card (card_id_number). and then determine whether the fines were paid for them all. borrow_date).
ON borrow (card_id_number. we want to determine whether the user has any unpaid fines before we let the user borrow the book. copy_number. In a large database. CREATE UNIQUE INDEX index14 ON fine (card_id_number. send_branch_code. We should violate normalization only if we have a very good reason for doing so. we will have to pull up all of the users borrowing transactions. when the book was due. When we move the fine information into its own table. we must give the librarian the ability to cancel a fine. copy_number). but we want to prevent a fine being levied against the user because of the librarys delay in logging the book. copy_number. ON user (ssn). the disk space we allocate to hold information about fines will be wasted. copy_number).First. receive_branch_code. then this look−up becomes very simple: when the user tries to borrow a book. in these instances. Indices As with our simple example. this can be a huge query.
CREATE UNIQUE INDEX index12 ON transfer (title_id_number. that will add up to quite a bit of disk space that is initialized to NULL. recompute whether they were on time. because the table fine shares so many columns with table borrow. INDEX index11 ON borrow (title_id_number. title_id_number. we will build indices for most keys. but this tramples on the notion of data normalization. If we graft the fine information onto the borrow table. The user returned it on time. copy_number). transfer_date). when a user tries to borrow a book. Furthermore. We could speed this transaction by inserting flags into table borrow to mark whether this transaction involved a fine and whether the fine was paid. most books are returned on time. ON copy (branch_code). For our first pass. CREATE INDEX index13 ON transfer (title_id_number. by dropping it into a book drop. This is a quick transaction that requires no recomputation whatsoever. For example. we check whether there are any records in table fine in which the column card_id_number matches that of the users library card and in which column paid_date is NULL. and the last thing we want is to make the system slow. it is best to move the fine information into its own table. the indices that we create for this database must balance the improved performance that an index brings. but it may not be logged in as returned until the following Monday or Tuesday. as follows:
CREATE UNIQUE INDEX index1 CREATE UNIQUE INDEX index2 CREATE INDEX index3 CREATE INDEX index4 CREATE UNIQUE INDEX index5 CREATE UNIQUE INDEX index6 CREATE UNIQUE INDEX index7 CREATE INDEX index8 CREATE UNIQUE INDEX index9 CREATE CREATE ON title (title_id_number). a person may have returned a book on Saturday. Thus. ON copy (title_id_number). title_id_number. ON card (ssn). One last consideration: When we design our system. As our library handles hundreds of thousands of borrowing transactions a year. with the cost of making and maintaining the index. INDEX index10 ON borrow (card_id_number).
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. why dont we simply add the columns for recording a fine to the borrow column and be done with it? This is a reasonable thing to do.

fine. copy. fine.
Step 5: Write domain−integrity rules
At this point. the status on the users current entry in table card must be changed to an appropriate value to render the card unusable. As with our baseball database. These rules are in addition to the rules of database integrity that apply by default.CREATE
copy_number.copy_number fine. it is not worth it. • A user cannot borrow the same copy of the same book twice in one day.
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. Note that MySQL does not allow you to build an index on a column that can be NULL. however.
We did not build indices on the following keys. or user. and we very much want to build an index for this column so that we can make this look−up as fast as possible. the system automatically levies fines for books that are returned late. it is correct to build indexes for such columns. as this example shows. If the user reports a library card as having been lost or stolen.paid_date will be NULL. If the card has expired. In this instance. INDEX index15 ON fine (card_id_number). However. so we very much want to find the instances where fine. the system will look up a users unpaid fines every time a user attempts to borrow a book.return_date
In addition to indices built on keys. the status of the card must be checked. If the card has been reported as stolen.card_id_number. • Finally. they will not be involved in many transactions:
branch.title_id_number.copy_number. The domain−integrity rules are rules that we will implement in software. • A user can have only one library card at a time. appropriate authorities must be notified. We could add a number column to table borrow that would allow a user to do so. we add one additional index:
CREATE INDEX index16 ON fine (card_id_number. branch. but we would have to track an additional column to account for a situation that occurs very rarely. under appropriate circumstances. For example. These are semistatic tables into which information is inserted only occasionally. weve finished most of the work of designing our database.receive_branch_code fine. if a book has lain in a book−return bin for several days before being logged back into the system. any fine that occurred during that period could be waived. date_levied). fine.
This index will help us to find when a user has unpaid fines: in these instances. This set of indices gives us a good start toward having a database that is fast. in our opinion. as experience shows us where the bottlenecks lie. • Before a book can be borrowed.paid_date is NULL. to help prevent nonsense from being written into the database.branch_name transfer. paid_date). one major task remains: to write domain−integrity rules for our database. Clerks can override fines at their discretion. fine. most relational database packages do let you do sowhich can be quite useful. we canand probably willchange our array of indices over time. yet efficient. the user must be denied the loan. This illustrates that even though a column can hold NULL cannot be used in a key. Study of the library problem and of our system suggests these rules: • No rules should directly involve tables title.branch_code transfer. because. the column fine.title_id_number.

As with our indices. the entities that live within the problem space that was defined in phase 1 are written. the above rules will give us a good start on building a robust. In this phase. and precise statement of the problem that the database is to solve. The chapter then discusses the art and craft of database design in translating the requirements of real−world project into a set of tables. Database design is a craft best learned by doing. built. and within budget. we must write down rules to help preserve the domain−level integrity of our database. These two rules are summarized in the principle of Boyce−Codd normalization. That is. and maintained correctly. To illustrate these principles. write a brief. but also a fair amount of people skills. In this phase. These rules help to protect our system from writing into the database data that cannot occur. However. In this phase. tested.
Summary
This chapter discusses how to design and execute a database project. In this phase. The database as a whole should avoid redundancy: no table should contain more than one instance of a column. and no entity should be described in more than one record. this chapter walks through two real−world examples of database design. designed. a table should contain only the columns that are part of the real−world entity that the table reflects. Experiencein the form of bug reports and customer complaintswill show us the rules that we missed. The emphasis is on project management: the steps needed to ensure that the project is planned. Most entities will have more columns than we have paper to write them on. Designing a relational database has five phases: • Step 1: Articulate the problem. useful application. This requires not only engineering skills. the columns that comprise each entity named in phase 2 are written. We have found two rules to be helpful when organizing columns into tables: Columns should be existentially related to each other. the bag of columns that we wrote in phase 3 are turned into a set of tables. • Step 5: Write domain−integrity rules. • Step 4: Design the tables. on time. as well as skill in maneuvering within an organization. simple.
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. our suite of domain−integrity rules probably is not complete. which states that every column within a table should functionally depend only upon the tables primary key. • Step 2: Define the information needed. This phase should result in a requirements document to guide the building of our database application. as articulated in phase 1. dictates the columns we select. • Step 3: Decompose the entities. After the tables that comprise our database are designed. the problem we are trying to solve. The chapter first discusses the planning and execution of a database project.

The criteria proposed in this chapter cover three rather broad perspectives of an organization: • Current data requirementsthat is. In this section we will take a look at how functions of an organization depend upon data (and therefore databases). departments. Converting to a generalized database is usually a straightforward task. This sort of data is well suited to both relational and object databases. or even in flat directories and listings. How will it benefit the organization? Who will own it? There are also issues surrounding the migration of old data to new database platforms. and executive decision−makers use administrative data. an organization must gain an understanding of the data to be managed. How will the old data fit into the new database schema? How can we move the data? These are frequently significant hurdles in the way of effective use of legacy data.
Evaluating Your Data Requirements
Clearly. That is the subject of this chapter. There is also the environmentbusiness and technologicalin which the database is to be used. departmental leadership. or collection queries. Human resources. such information is often found in spreadsheets. object−oriented path expressions. Let us look at some possible classification of data for a typical organization. what is redundant and what is missing. Administration This includes information on the personal information and benefits of employees. 159
. Not as clear to many organizations just starting out using databases as a strategic asset is that there is more to the decision than this. and how the data itself and the use of the data changes from function to function. and the classification of employees.
Business categories of organizational data
The data that organizations manage can be classified in many ways. It could be queried with basic SQL relational queries. Administrative information tends to be organized as a series of records with similar format that is related hierarchically and by basic classification. you will need to have a firm understanding of the criteria for choosing one database product over another. proprietary human−resource and contact−management software. with respect to choosing a DBMS. If not already in formal databases. as do employees. from legacy systems that are being replaced • The environment in which the database will be operatedfor example.Chapter 5: Deciding on Linux Databases
Overview
Before you can make a choice about which Linux database is best for your needs. to examine benefit information. the requirements from this point forward • Existing datathat is. which may include evaluating the skills of the personnel who are expected to administer the database. the personnel hierarchy. Implicit in this discussion is the need for ongoing assessments of how well the organization makes use of its database assets. and whether the existing database infrastructure is a hindrance or a help. information on job applicants. the technical infrastructure.

the monies owed to the organization. An organization that tracks and accounts for the expenditures and receipts in a way that is compliant with accepted accounting practices. The actual list of attributes and entities involved is rather lengthy. This can be an onerous restriction. and regulatory requirements. these will be the customers. Again. many organizations manage their accounting data with interlinked spreadsheets. payment history. Accounting data tends to be organized in tabular format organized by date and basic categories. Other important information contained in an accounts receivable system are credit history. as many of them adopted the computerized version of the classic spreadsheet model for their financial records and projections. and so on). as many companies found out when the European Union adopted the unified currency. what part of the organization and which general ledger account. In fact.
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. Typically. it is in the general ledger that an organization sets up budgets. The general ledger is the place where every accounting transaction ultimately ends up. For some organizations. primarily from accounts payable and accounts receivable. money owed to vendors. If not already in formal databases or specialized financial packages. credit rating. For example. what was purchased. that is. and shows stockholder equity. The author has even seen general ledgers being used for the recording of the amount of industrial waste (yes!) generated because this was a required report by regulatory bodies. was one of the first computer developments to affect organizations of every size and profile. determines profitability.
Accounts payable
Accounts payable contains the transactions for obligations. which department is being charged with the payment. compares actual expenditures and receipts to budgeted expenditures and receipts. the general ledger accounts to be credited/debited with the receipt will be of importance here. the payments themselves. as it applies to the corporation as a whole. customer information (contact names. employee compensation. and income taxes). in 1998. records depreciation and appreciation. when the payment cleared. records balance accounts. such as the Financial Accounting Standards Board (FASB). for example. who approved the payment. such as Securities and Exchange Commission (SEC) and Internal Revenue Service (IRS) rules. phones. use. Financial data includes these three major areas. addresses.
Accounts receivable
The other side of the coin is the accounts receivable. The accounts payable systems include such information as the vendors to whom the payments are made (including government agencies for obligations such as sales. and the payments that are made for each of these obligations. a voucher number that approves the payment for an obligation identifies an account payable transaction. it does so primarily through a general ledger application.
General ledger
The general ledger contains the accounting transactions. the advent of the spreadsheet program VisiCalc on the Apple in the early 1980s. purchases of material. Primarily.Financial information systems Financial information systems encompass the majority of the applications that one will find in organizations of almost any size. accounting data is particularly dependent on currency and exchange rates. and which general ledger account(s) should be credited/debited with the payment. the euro.

Another scenario is to have some product data actually exist only in marketing and sales material intended for internal or public distribution. the choice is most often for an off−the−shelf package that provides a turnkey (ready−to−run) solution encompassing and integrating virtually all of the functional areas imaginable. and Resource Planning. These files may be comprised of schematic drawings and parts lists. To integrate these files with a relational database management system (RDBMS). Shipping. marital status. competitor and marketplace information. Marketing and customer data Marketing data includes survey and product−registration responses. nonprofit concerns. product data is geared toward enabling those applications that produce online catalogs and that support e−commerce. it is often highly integrated with the operational data that pertains to the processes for developing. producing. and descriptions of the various products put out by an organization. Luckily. For the larger organizations. object and universal databases provide approaches to simplifying the management of such data. for example free−form text responses to questionnaires. The incorporation of nonstructured data introduces some challenges. and the like. Marketing data is usually entirely intended for statistical analysis. In manufacturing firms. Frequently. and Warehouse. the data used by marketing is purchased from vendors who specialize in this kind of service. but such efforts bring great benefits. Marketing data very often consists of collections of data in a variety of schemes and formats. Although clearly relevant to manufacturers of various kinds. theres an obvious risk of losing track of when or where such information can be found. one can send out a list of customers and receive back this list with additional information such as income. such is the real world! Product information is used by marketing and line−of−business staff and manufacturing management to direct day−to−day activities. comptrollers. The eventual choice often has great consequences for other database decisions. including Personnel. and so on. Analysts. and incorporating unstructured data such as textual descriptions. Product Product data includes specifications. It is not at all unusual to find product design and manufacturing data in specialized file formats.Choosing database formats and management systems for accounting data is typically a very serious task with numerous factors to consider. and supporting these same products. as businesses have lately discovered. Purchasing. and by executives to determine overall enterprise strategy. Customer support agents use product information to help customers. to the file(s) as one of the attributes of a database record used in a product manufacturing application. and schematics. But. Timekeeping and Payroll. In this event. pricing. even this kind of data can be made accessible in a practical way in a RDBMS. and information on prospective customers. For example. It can be difficult to mold it all into a unified structure. Material. Accounts Receivable. and from numerous sources. and management at all levels use accounting data in the decision−making process. Some analytical techniques. General Ledger. pictures. with the appropriate preprocessing. Increasingly. Product data tends to consist of distinct records using complex categories. Survey data can be somewhat more difficult to manage with the usual RDBMS structures because so much of it is textual in nature. Sales Order Entry. However. age. products can also be used abstractly to denote services. part numbers. you would store a pointer. such as a URL or file system directory path. such as data 161
. A second source of marketing data comes from surveys of every kind imaginable. Accounts Payable. Distribution. government functions. categorization. and this requirement has a significant bearing on the chosen database management system (DBMS).

Consumer Affairs. consultancies. the key data managed includes customer contact information and purchase histories as well as records of customer complaints. Operational data takes many forms and comes from many sources. Most generally. the operational details of a given organization tend to be as distinct as a fingerprint. flight and maintenance schedules. and there is an entire series of industries that has emerged to provide tools for this purpose. Universities. In highly regulated industries the business rules might to a large extent originate outside the organization. grades. it includes course listings and schedules. having a system that can export (produce) a flattened (fully denormalized) version of an organizations customer data for analysis by some specialized statistical applications is valuable. Operations Operational data is very hard to generalize. it includes seat−maps. For instance. In the airline industry. with various approaches to implementing a database management system. comments. and grade−point averages. advertising. along with student registrations. responses to marketing promotions. In manufacturing firms. The process of gathering. interestingly enough. for instance. it changes dramatically in character. And so on. sales. Research and development Some organizations gather large amounts of research data. and managing this data usually depends on the systems employed in managing other types of organizational data. and it is analyzed by management to determine customer trends and anticipate crises and improve market positioning. with mathematical relationships. work most effectively on flat−file layouts that are. Between broad categories of organizations. but recent management theory highlights the importance of handling customers in a holistic manner. Line−of−business staff and general management use operational data. Research and development data often comes in tabular form. and so on. healthcare organizations. Even though there are subtle differences between processes and approaches in each segment. These industries go by names such as Customer−Relationship Management (CRM). In some industries. improve the efficiency of marketing and promotion activities. It is usually 162
. Customer data is used by marketing research. government. Even within one vertical segment. the antithesis of RDBMS practice. and crew assignments. Customer data has traditionally been a synthesis of data from marketing to accounting. transportation. and the parameters and rules for general management process. and armed forces are a few examples. marketing data is often found in flat tables. business rules could be aggregated into an inference−engine in order to automate many line−of−business decisions. and product testing. It is usually the key information that drives enterprise strategy and market positioning. faculty assignments. or incorporated into customer−relations systems. operational data incorporates asset and equipment inventories. psychographics (attitudes). and customer support to streamline customer contact. So. and Customer Master File applications. a good deal of operational data consists of business rules. it includes job scheduling and supply chain management data. the rules would often be encoded into a format based on formal logic. preparing. demographics.mining. Research and development data comes from scientific experiments. surveys. If not already in a formal database. which come with their own peculiar database demands. If not already in formal databases. In universities. think tanks. In this case. which might be familiar to those of you who have worked with the prolog computer language. customer data is usually found in custom software such as call−center toolkits. and requests for help.

managed with highly specialized applications with powerful statistical and scientific analysis facilities. the idea is useful to organizations of all sizes. as you might imagine. flat documents. documents are essentially unstructured. Documents. and further down to subsections and document fragments. The basic problem is that with the data disorganized. However. and modern tools. such as airline manufacturing. pagers. Doing so inexpensively and securely requires great attention to document−management issues. This is the idea of designing a unified set of intranet sites that enable employees to access enterprise information using searches. While EIPs are technically more the interest of very large organizations whose vast collections of internal data make such portals somewhat of a necessity. This is a typical arrangement that suits many businesses. A recent catch phrase in Information Technology (IT) is the enterprise information portal (EIP). categories. or you may just have data scattered about a clutch of small DBMSs. and other such appliances. Electronic document management Documents are often neglected in a discussion of organizational data. Managing documents is a great problem in computer science. proprietary software. Quality assurance personnel use R&D data to make decisions about product readiness and manufacturing process. including DBMS products. This suggests a structure similar to nested containers or a collection of trees (a grove). although recent trends encourage greater structure for documents. The huge success of the 3COM Palm Pilot and the move of such technology into cellular phones. but this is an unfortunate oversight. has encouraged database vendors to develop versions designed to work on such small−scale devices. Research and development (R&D) data is used by line−of−business staff to inform daily decisions and marketing for product promotion and general public relations. a vast category. there are good reasons for an organization to want to develop an overall database strategy. site maps. and Web−site material. They can be imagined in a hierarchy from document class or template.
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. document management is not a concern.
Assessing Your Existing Data
If you are evaluating a Linux database for your department or small enterprise. or in a framework that allows easy export to small−scale operating system databases such as the database built into 3COMs PalmOS. while for other organizations. The growth of the Web is boosting the appreciation of document management as companies struggle to arrange their documents in a coherent form online. gathering data for such basic processes as budgeting and employee orientation involves undue effort and expense. internally for employees. The big impediment to managing documents electronically with the same flexibility as is found in RDBMS is that. or with the public. from marketing white papers to shareholder reports. This allows great flexibility of information access and entry if all the organizations data is stored in an applicable universal database. to individual document. from the perspective of available database management systems. Some industries. range from employee handbooks to product manuals. provide improved document support. Some organizations are driven to a more formalized database structure by the advantage of using universal connectivity to enable mobile users to access the databases using the emerging class of personal communications devices. within a group of partners. and hierarchies. you may already have an overall database methodology. have tackled the problem with great commitment and at great cost. Documents come in varying levels of structure. spreadsheets.

This is no different from any other networked machine. including commercial products such as Oracle. the DBMS is much more secure from unauthorized access from outside. Such DBMSs have a server module that maintains the actual persistent data store. isolate the DBMS address and port. a malicious person.
Figure 5−1: Outside firewall
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. all the DBMSs more closely examined in later chapters of this book are of client−server architecture. and use various methods to gain access. But network security is important even if you are not using all the network facilities of your DBMS. Many DBMSs leave the network port open. and that provides a network interface to which various client applications can connect. If you are to use a client−server database. Normal security precautions are required in either event to secure the database via log−in identifiers and secure passwords. even if the clients are configured on the same machine as the server. We presume that in both cases the intent is to allow the internal network to get through the firewall to the Web. in this case from the World Wide Web. so this has not changed in either case. but inexperienced system administrators sometimes forget to protect their DBMS server. might be able to access your data. In fact. Sybase. In this case. and Adabas.Environmental Factors
If you are planning a database strategy. as well as Open Source (see Chapter 1) products such as MySQL and PostgreSQL. If not. Figure 5−1 shows how a security breach of the Web server can allow unauthorized access to the DBMS from an outside attack. you should consider several factors beyond your existing data. The first issue that this opens is that of network security. or cracker.
Network infrastructure
Client−server DBMSs are currently the most common. Note that in this case the internal network could still be a source of a security breach. a cracker could scan the ports on the server. Many databases are set up as part of Web information systems on the Internet that are completely unprotected. In Figure 5−2. it is important to ensure that only authorized users can connect to the database server. with the same components in a different configuration. The general solution to this is to make sure that your DBMS servers are behind a firewall.

and the availability of specialized Linux systems administrators increases with the popularity of the operating system. Minor changes in the administration of such systems can have far−ranging effects on performance. Open Source DBMSs are not as demanding of maintenance staff. this is a quickly growing area in Linux. Again. as well as such authentication methods as S/Key and biometrics. are looking to host database servers entirely for their clients. Some. including some knowledge of security.
Technical staff
All databases that see any use require maintenance. DBMSs still need to run on an operating system. Another possibility is to employ third−party training to prepare administrators for the anticipated introduction of new technology. One possibility is to hire a consultant for OS and DBMS management. especially those who are novices with Linux and/or UNIX. Despite Oracle Corporation's efforts to make the operating system obsolete. this will be less and less the case. In fact. As they gain more features.Figure 5−2: Inside firewall Crackers with access to your networks present another danger: they may use snooping devices to compromise your passwords. Remember that even if a cracker cannot get your passwords or snoop on your data. and even Internet Service Providers (ISPs). and the major 165
. Naturally. it should be enough to have technical staff with experience in UNIX. important. with the various certification and training efforts announced recently. The best defense for this is rapid detection of denial−of−service attacks. many more data−center specialists. ranging from automatic approaches such as clustering and redundant hardware to failure detection and instant administrator alert for remediation. Apart from security. It is important to be sure that you have experienced system administrators to maintain the operating system. Currently. you will want to make sure that your network is robust enough to handle the volume of traffic that your applications will be generating between clients and servers. such as the large enterprise databases are legendary in their need for specialized training and experience. but that is because they have fewer complex features. You will want to arrange some sort of failure−recovery procedure. they may still employ a denial−of−service attack to disrupt your systems. When deciding on a database strategy it is important to consider who will be maintaining the databases. DBMS software requires varying levels of expertise for administration. specialized Linux support is even better. encrypting all network traffic is usually a good idea to prevent sophisticated crackers from reading sensitive data right off the wires. This is understandable as many of them are themselves as complex as operating systems. For Linux databases. This makes encrypted passwords. In fact.

DBMS vendors have long had extensive training and certification networks. such as the processes of hiring and terminating employees. Issues such as backup and security are also significantly affected by cross−platform issues. When an organization needs or desires to make use of data from old systems. but they can be very expensive and many organizations choose to simply roll their own with scripts. If so. The question of available expertise comes up again in these contexts. For example. We have proposed that there are three areas that need to be considered: existing data and uses of the data. it is of prime importance to determine how the old data will fit into the new structure. the introduction of a new operating system and network protocol (Linux with TCP/IP) can mean additional training for an organization that doesn't have personnel with the required skills besides the issues of cross−platform access to the data. From a technology perspective. To take these events as examples.
Cross−platform issues
Your database strategy might involve several DBMSs and host operating systems. The third area that is of importance when considering a Linux database is the environment in which the database will be used. whether it is an accounting system or a human resource system. you will need to consider the ease and expense with which your data can be exported to EDI formats.
Organizational processes
You must also consider what processes are in general use in your organization.
Summary
In this chapter we have presented an organization from the perspective of the need to decide on a Linux database. It may be that the old data is left as is because the cost to convert it to the new system is too high. the fact that it will run under Linux can prove to be a substantial obstacle for an organization that has a corporate standard of using Microsoft products only. For instance. There are many software and hardware solutions for turnkey cross−platform backup. are relevant. There is much less available for Open Source databases. and the security infrastructure that such a change in doing business requires. A third area that almost seems implicit when considering a Linux database is when an organization starts allowing customers and suppliers to have access to some portion of the organization's formerly inaccessible data. and the environment−physical and organizational−in which the data is managed. When an organization is evaluating its data requirements for the present and the near term. Other organizational matters. such as internal data representations and encoding of data exchanged between subsystems. These processes determine how your data is updated. 166
. if you use Electronic Data Interchange (EDI) in your cooperation with vendors and partners. while terminating an employee would involve removing all simple opportunities for sabotage or theft of data. data from obsolete applications. Your DBMSs should support user and account management systems that readily incorporate into your organizational process. it is important to consider issues that may occur while trying to integrate these systems. it is necessary to understand the distinction between the data needs and the uses of the data by parts of the organization. and with what external systems your data must interact. how reports are generated. hiring an employee might mean giving the employee access to particular portions of the database.

that may be the implemented solution. forgetting all about the real−world problem that you are trying to solve.
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. and configuring your database system. This is a crucial step in designing your system. then a lot of the lower−level decisions may already have been made for you. The real goal of the human resources database is to make it easy for users to find the information that they need to know the employees in their organization. Stating the goal of your system identifies for you the main objective of your project. and if you are just beginning to build a new application. If your shop is already set up. As a developer. you may want to extend the database management life cycle down to the level of choosing and setting up your hardware. Ultimately. and document the reasons that you have for putting each constraint on your project. If you are starting from scratch. For example. Keep a detailed list of your constraints. and help you to identify the needs and requirements of database systems in general. but this chapter helps you to look at the big picture and to address common database issues in a general way. your goal is the same.
State your goal
Take a step back and try to look at the problem as a real−life situation. It provides a general set of guidelines to follow while planning. It will give the user the information they want. the important thing is that you end up with a system that does what you want it to do. you will have plenty of opportunities later to make decisions about how your data will be best organized in the database. planning. even though the two tables can be joined to relate each person to the department that he or she works in. installing. Start deciding on the guidelines that you will follow while trying to build a system that accomplishes your overall goal.Chapter 6: Identifying Your Requirements
This chapter will help you to understand the process of building a database system. selecting. These steps help you address the issues involved in building a good database system. we are simply trying to figure out why we want a database system.
Introduction to the Database Management Life Cycle
The database management life cycle is a general set of steps involved in designing. you want to build a database system that meets all of your requirements and conforms to all of your constraints. not as a new computer or database. and what we want it to do for us as people. Greater detail is given about much of this information in later chapters. A human resources database system should not be designed so that it stores personal information about employees in one table and the departmental information about the organization in another table. This cycle can be extended to reach various levels of system setup and design depending on your specific needs. it's time to think in more detail. After all. let's look at a human resources database system. Either way. This goal is the one thing that you must keep in mind with each decision that you make that is related to this project. project. but it is not the goal of the system. Once you identify your goal.
Identify constraints
Your system must accomplish your goal−that is the most important thing. Right now. It is too easy to begin designing a project by getting right into the guts. and building a database system.

they are the rules that you have decided to follow. you can begin to think in more technical detail. and it's time to start thinking about how you are going to do it. Remember to have your constraints and overall project goal handy when you are working on and discussing the different solutions. At this point. At this point. you know what you need to do. Stating them clearly in the early design stages of your system will help you to avoid backtracking when you get into the later development phases of building your database system. think of them as guidelines that you are setting for yourself to follow. You may want to lay out a few possible solutions. and begin designing your database system. Communicating your ideas with others will help you to see things that you won't notice on your own. Defining strong guidelines for the application up front will help you tremendously when you finally get to start the development of your project. and straying from them now will cause you a lot of confusion during the later stages of design and development. There are a whole variety of things to consider when building a Web−based database system. Also. Now is a good time to figure out what types of client programs will be used to access the data in your database. If your system will be run on the Web. remember that these constraints are not to be set in stone. I know that's what you have wanted to do all along. you should use it. and decide what language you will use to write the applications. then you should consider redefining that constraint. If your project has a deadline. operating system. You will have to decide whether you are going to use server−side CGI (Common Gateway Interface) programs or servlets. The guidelines are just another part of your design. and what protocols the client applications will use to communicate with the database server. in this context. or budget. and they are covered in more detail in later chapters. and then discuss them with others in your organization to see which solution will be best to use. should not be thought of as limitations. or whether you will use client−side Java applets that will be downloaded and run from the user's machine. then you should make notes of them also. Organizational constraints Define any organizational guidelines that you are required to follow early in your design. Figure out what language the client applications are going to be written in. Define the client machines. and network protocols.Constraints. so 168
. As you can see. Now. you can start to lay out your requirements. in terms of hardware. instead. When an alternative design better fits the solution to your problem. All of these factors will need to be considered when defining the solution to your problem. there are many factors that must be considered when building a client−server database application. In general. Identifying them now will help you to know exactly what you have to do later. Organizational constraints are usually easy to define. then the only client you have accessing the database may be the machine running your Web server. and if you find that a constraint limits your ability to meet your end goal. and hard to change. Application constraints You also need to define other guidelines that will be required of your system. If your organization already has a database server in place that you are required to use. and will also give you fresh insight to the problem at hand.
Layout requirements
Now that you have a detailed list of constraints. You will still need to know what type of system it is. you need to lay out how you expect the system to work. then note that as a constraint.

and we have identified the tools that we will use to meet our goal. but you don't have anyone around that knows how to program that language. it is time to determine whether what we plan to do is possible.
Finalize your requirements
This is the part of designing that seems the most practical to developers. or even thousand. finalizing your requirements. In general. The idea here is to torture test your design. identify obvious relationships. then it's time to figure out which one you want to use for the project. Choosing a database to meet your needs is discussed in detail in Chapter 7. lines of code. you will want to find it at this stage of your development. You should also know and understand the data that your system is being designed to store. Draw diagrams of these layouts. It is much easier to identify problems before they happen. you are ready to move on. Now that you have all of this. and how that software is going to communicate with the database. You should know what database server you will use. Talk to the future users of the system and make sure that you understand the data well. than it is to have something sneak up on you when you think that you are almost done with the project. Don't feel bad about the amount of time that you spent on this part of your project−it will have been well worth it when you are finished. and what type of machines the client applications are going to run on. and how it all fits together. Now that we have the goal of our project laid out. then be happy that you found out now. you want to select a database that fits well into your organization and that addresses the needs and constraints of your problem comfortably. Remember to be practical when making these decisions. and how your client applications are going to communicate with the database server. all of this planning will be carried over directly into the later development stages of your project. we have to determine whether it's a practical solution. You should also pick a product that will expand to meet your future needs. Get to know your data.
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. and define the relationships of the data. After we decide our design is possible. Now it's time to move on to the next level of detail. If your design is good. and the language that you are going to write the software in. Just imagine how you will feel if you have to throw away a few hundred. You also have to decide which programming language the application software will be written in. If there is a potential problem. During this step. If your research tells you that a particular language is best for a project. and begin to lay out some possible table configurations. you should finalize many aspects of your system.go ahead and have a go at it! If you don't already have a database server. You begin by thinking about how you will store the data in the database. That's when you will wish that you had spent more time planning. At this point. or that it will not meet your end goal. what language your client applications are going to be written in. Chapter 13 discusses several different languages and protocols that can be used to communicate with the databases from client applications. and then try again to identify any areas that can be improved. you know what database server you are going to use. You are going to have to live with your decisions for a long time. so try to make comfortable ones. If you discover that your design is not good. then it will probably not be the best solution for your organization. Choosing a database server is another important decision that can get very complicated.

and will feel some accomplishment each time you complete one. a database server can be a very complicated system that is capable of doing all sorts of things. and the response is the database's reply to that request. This part of your project should be straightforward. If you want people to have access to your data from other machines. the moment that you have all been waiting for−let's start developing the database system! At this point. and you can concentrate on all of the little details. In the most basic form. without even realizing that you were outlining your development plan. In practice though.Plan your execution process
You are almost ready to start building your system. and that you document any deviations from it very carefully. all you have to do is start it. That way you will have several short−term goals to focus on.
What is a database server?
In general. If you are working for someone else it might be nice to show them this plan so that they know what you are doing. that's all a database server is. If you have a development team. Now. But before you jump in. Everything should be right there. You think that you have already done too much planning for this project. A program 170
. If you ever need to know what to do next. When the program receives a request. and to make a timeline of when you expect to have different stages of your project finished. and you would probably have done it anyway. Now is when you make a schedule for what needs to be done in order to implement your design. The request usually asks the database to do something. then you will need some form of remote access. We suggest that you stick as close as possible to your plan. Because every system is so different. assigning different sections of the project to your developers. and planning well for its execution. listening for requests that will be sent to it. just take a look at your schedule. and when to expect the different phases of your project to be completed. it interprets that request. a database server is just a set of programs on a computer. you can divide the work.
Assessing the Requirements of Your Database Installation
The requirements of your database installation are based on the needs of your system. with an area on that computer's hard drive that these programs will use to store data. and responds to whoever made the request accordingly. it will still help you to divide the work into distinct parts. and it waits on your computer. then you are going to need a lot of disk space. We are just suggesting that you pay a little closer attention to something that you were already going to do. It is really a small step. The requirements of your database installation are specific to the problem that you have already set out to solve. These steps will help you to manage your time and to figure out when different stages of your project need to be completed. One of these programs is usually called a daemon. If you are doing all of the work yourself. clearly laid out for you. Isn't it nice to not have to worry about the big picture as you do your day−by−day development? This is just one of the great advantages of starting with a good design. there really isn't that much to say. If your system is going to hold many gigabytes of data. you need to outline your plan of development. you will know exactly what to do. and planning how you will implement your plan sounds silly. You have planned everything out so carefully that you know exactly what you need to do. There are other programs on the computer that are related to the database and that do other things.
Build the system
Now.

you should always start by carefully reading the system requirements and installation documentation. and is not given any rights to other areas of your system. the program can give complete access to your database. Regardless of which database system you are installing.
Set up a user account
Database servers allow remote access to your computer. There may also be other utility programs that are part of the database server.
Read the documentation
Each database has its own set of installation requirements. It is commonly called an SQL monitor. users include anyone who even uses some client software to connect to your database. Now you can see how your database server is starting to look like a little more than a program and a section of your hard drive. then the user of your database can be anyone on the Web. A second benefit that having the database server run as a special user account is that administration of the Linux system is made slightly easier. The people who wrote the software thought the documentation was important enough to write. This account is given full rights to the parts of your computer that have to do with the database system.that allows users to directly interact with the database almost always comes with a database server. an account is created solely for this. Many RDBMS systems run the query processes against the data as the login account used for installing the database. or programs that help you to back up your data. But like any software. of the running Linux processes are database processes. Most of the database servers that we are covering in this book run on your system under a special user account. If one of these users figures out a way to compromise your database system. it prevents users of your database from gaining unauthorized access to your machine by putting them into a controlled environment. to anyone who knows how to take it. Having your database server run as a separate and dedicated user provides two benefits. so you can be fairly certain that the information there is important enough for you to read. and it is how you access the database server manually in an interactive way. or to your entire computer system. if any. So. or simply programs that start and stop the database server safely. This is as opposed to database processes having the current login user identification that is more difficult to use when trying to identify which. and then display the database server's reply back to you. if it is not correctly configured. and it will protect against unauthorized access to both your machine and your database. that of the RDBMS.
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. Typically. The SQL monitor usually lets you type in commands that get sent directly to the database server. they may be able to gain access to your machine through the database server. First. when using system utilities that display user activity the database activity is easier to identify and monitor when the processes are owned by a single user account. If you have a Web database application set up. By design. Having your database run as a special user will limit what they can do to your system should this ever happen. Note Remember that the users of your database are not only the people to whom you have issued database accounts. and we all know how much developers dislike writing documentation. This is a good way to have your system set up. they are supposed to allow only known users to perform specific tasks on your system. They may be programs that help you to do things like copy large amounts of data to or from the database.

will give you enough information to decide whether or not you can support the system. For now you need only a rough calculation. We're talking about 3:1 or 4:1 initial estimates. the application developers need to provide the requirements for temporary space consumed by the queries. configuration files. and roughly how much data you want to store in your database. it is best to conclude that you don't have nearly enough storage space! Knowing how much space the database system needs. and even though you have extra room today. plus index space and temporary space needed by query processes. and the size of the database rarely ever grows or shrinks. In this type of situation. This type of database is easy to plan for (although not really very common) A second type of database is one that grows and shrinks regularly. and how the data is expected to grow over the anticipated lifetime of both the database and the applications that use the database. It is helpful for you to know all you can about your data before you set up a database system to store it. and possibly table temp space for user queries and application queries. There are ways to calculate exactly how much space you will need for your data and database. and the minimum database storage area. This information is necessary for you to plan not only for the data storage needs over the years. but they go beyond the scope of this section of the book. it is uncertain whether you are going to have it tomorrow. Different types of data grow at different rates. Cross−Reference We will discuss all of these issues in depth when we get to the second part of this book. or you will have problems. the number of users that can be supported. The term 'database' is meant here to cover both the logical database as well as the particular instance of the Linux RDBMS. Each database system needs enough disk space to store its server and utility programs. If the estimated need is 60 percent or more of what is available. documentation.
Amount of data and data growth
It is an imperative that you know how much data you will need to store in your database. but also for back up and recovery strategies. and so forth.
Classification of Information and Data Needs
Data comes in all different shapes and sizes. You should find out what type of data will be stored in your database. Make sure that you take into consideration multiple queries running simultaneously! Each database server has its own space requirements for the system program and configuration files. and configuration information.Assess disk space
The database server needs disk space. Some databases hold a set amount of data. application planning. migration strategies. as well as how the user intends to manipulate the data and what the user expects to gain from having the data in a database. These databases are hard to plan for. but not at a necessarily set rate. you have a fixed−size database. You should be able to find out how much space is required by reading the documentation that comes with your database server. This type of database may store transaction information of some sort. Pay close attention to the variations in this type of database. or some type of information that varies frequently.
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. as well as additional space to store the data that you are planning to keep in your database. That will be enough to determine whether some existing mass storage will work for you.
For the purpose of assessing whether or not an existing configuration of mass storage is sufficient you only need a rough idea how much space the database will require for its system programs. If there will be application programs using the database.

full data recovery and uninterrupted service are probably the most important features. and care should be taken to make sure that the data in the database maintains its integrity and stays safe. Storing data of this nature involves frequent backups of the database and very high security for the server that it runs on. Be sure to perform regular backups. and will need to be treated as such. your Web site log data. these databases usually hold important information. If you completely lost your database it might take you longer to restore from a dump. At the same time. On the other hand. then someone else is already making sure that the data is accurate. you are using the database for its capability to easily perform complex searches on your data. than it would to for you to re−create the database from scratch. it is about how replaceable your data is. Two common types of database systems are transaction systems and decision support systems. the data may not even be your own. good at all. These databases grow as data is collected. and make sure that this database always has enough room to grow. or backup. A repository−style database might hold customer information. That makes the data very hard to recover in case of a failure. In transaction−based systems. or it may be very replaceable. Defining what type of system you plan to implement will help you make better decisions for your specific needs. Asking about data replaceability can bring a different answer than asking about whether you need the data to begin with. Maybe you are just putting the data in a database so that it can be easily searched or referenced against. In this situation. if your data is something that you keep in a database for convenience. then your data is probably very important.
Importance of data
Importance of data is not about whether or not you need the data. frequent backups would do you very little. Each type has different features that are important to it.
Common database activity
What do you want to do with your data once you have it in the database? This is another factor that will help you determine the features that you want in a database system. but what if you were making a deposit? In that case. and would lose value if it were removed. or the database's capability to relate this data to some other information that you have stored somewhere else. or some other information that is used for archival purposes. Rather. Consider the classic bank account example. This is where data gets added to the database but is almost never removed. In this case. With transaction−based systems the data stored in the database changes frequently. and are expected to keep it there. If this is the case. then it may not be as important. and properly archived. and without administrator interaction over periods of time. Determining the importance of your data is a necessary step in deciding what features you need in a database server. if any. The programs that access the data will need to be very carefully planned out. In some cases. This is especially true if you have scripts written that automatically handle the updating of the data from a downloaded file. Would you want your bank's database server to go down before it had a chance to record a transaction in which you just withdrew several hundred dollars from your savings account? Maybe. but it might be something that you download from a public data repository regularly. If your data is a collection of all the work that you have done over an amount of time. we are sure that you will want to know that your bank has the capability to fully recover from any type of database failure.Another common use of a database system is as a data repository.
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design. but will your business come to a screeching halt if you lose it? Probably not. If you can. Is the data very important to you? Maybe. A good goal is to try to use about 85 percent of the total capacity of each resource in your system. and any one that you choose will most likely be enough to get you well on your way. It's not always easy.
Processor
You only need enough processing power so that you can use the other components in your system. Your system will only perform as well as its weakest point. Decision−support systems are commonly used to help people make important decisions. However. memory. you might use the information to target your current customer base when advertising specials or sending out coupons. Join the club−most database developers try to find ways to make their systems use the best features of both types of systems. but deciding where you fit between these two types of systems will help you to make some very important decisions when setting up and configuring your database server and system. At the same time. and backup media. It is very hard to predict what kind of processor load your system will be under after it's up and running. The hardware you will use to run your database system is what brings your plan. The memory needs of different database servers varies. don't feel too bad if you have to make a blind estimate on your own. you might use this data to find out in what geographical areas you might be able to find new customers.
Memory
Memory is another tricky factor to consider when building your system. Thousands of different searches could be done on your data. Follow the guidelines laid out in the documentation for your database server carefully for specific memory configurations. in these types of systems. If you are trying to expand your customer base. ideas. Modern processor speeds are very fast. and you will want a system that makes that as pain free as possible.
Choosing the Proper System and Setup
Deciding which is the proper hardware for your system is heavily based on all of the decisions that you have made so far. It never hurts to have too much memory. so you are going to have to estimate your needs. and get the information back very quickly. possibly by asking for their zip code at the checkout. but adding memory to your machine will not always be the solution to poor database performance. Having a super processor in your machine won't help you very much if slow disk access and low memory resources never let it work at more that 20 percent of its full capacity. and ask them what they recommend. Odds are that your database needs fall somewhere between these two types of systems. If you are a retailer and you track where your customers live. disk storage. you should talk to other people that are running similar systems. then every day you collect a lot of data.Data repository and decision−support systems are usually much easier to recover in case of a database failure than are transaction−based systems. but there must be a reason why you are collecting it. All of the planning that you have done so far will be for nothing if you implement it on inadequate hardware. and the server's documentation should 174
. If your business wants to focus on customer support. Don't put all of your resources in one area of your system and starve another. The important thing to remember when configuring your system is that you want to keep it balanced. it is very important to be able to perform complex queries on your data. Sometimes it might even be faster to re−create a data repository from scratch. than to restore the data from the database's logs and backups. The main areas that you need to focus on when deciding the hardware requirements for your system are processor. and programs to life.

Mirroring will not directly help with database performance−it may actually slow your database down−but it will help drastically with data recovery. RAID is a group of individual small disks that act. the disk is where your data is being stored. The database server is constantly reading information from the disk into memory. If you have a lot of data going to and from your disks. If you notice that your system often needs to use swap space. if one disk fails. and should spend your time trying to optimize processing and disk I/O. All of the data. There are different types. But when you have a lot of data that you want to read from the disk. The major problem with having data stored on a disk is that it is read and written to and from the disk sequentially.give you guidelines to follow on how much memory is adequate in your environment. Adding disks to your database system is like opening another cash register in a grocery store. You can understand the problem if you think of it like the checkout line at a grocery store. If your system never needs to use swap space. because it has to be put on two disks each time a single piece of data needs to be saved. as one single large disk. The specific configuration for each of database server is different. Mirroring is the concept of storing a single piece of data on more than one disk. or a RAID (Redundant Array of Independent Disks) system. Another advantage to using multiple disk drives for your database is the capability to mirror your data. For now. are free to move through the checkout line much faster. When there is one cashier (disk drive) checking out all of the customers (data) in the store. of RAID configurations. the cost in 175
. especially in case of a disk failure. Configuring your database system to use multiple disk drives effectively is a lot of work. However. or customers. you will see a major gain in performance by spreading that data out over several different disks. it should be enough for you to set your system up and watch it run. and writing new information back to the database on the disk. But when another cashier opens an additional cash register the line moves faster. and interface.
Disk storage
Disk I/O is a huge portion of your database's overall function. so being able to access the disk quickly will improve the performance of your database system. You can have full control over what parts of the database are placed on the different drives. Single drives Multiple individual disk drives are nice to use when setting up a database system because you can configure the server to use them exactly how you want it to. This is fine when reading small amounts of data. The efficiency with which your database server can read and write data to and from the disk has a big impact on your database's overall performance. the line (data) moves very slowly. which leaves room for error. There are two types of configurations that you can use to spread the data in your database out over multiple disk drives. The performance loss with disk mirroring is only associated with writing data. We will discuss memory issues related to each database server in more detail when we talk about configuring database servers later in the book. After all. the read head runs over the disk to pick up the data that it wants and it's done. you most likely have enough memory. then adding memory will probably improve your database system performance. the data is still available from another disk. or levels. comes the hassle of having to setting it all up. giving you a lot of control over how the database performs its physical reads and writes to the disks. and lends itself to different situations. and if not done properly can actually reverse the performance benefit that we are trying to gain. You can use multiple individual disk drives. with all the freedom and control to configure the disks the way you want. you have to wait while one device does all the work. Memory needs are mostly based on the structure of your data and the types of operations you will be performing on it. This way. In most database situations. Each configuration has its advantages and disadvantages.

which we just talked about. Most backup plans that offer full. When your RAID does both striping and mirroring. RAID level 0 is disk striping. and some vendors even guarantee. ever. use your favorite Internet search engine to search for 'RAID Definition. Setting up individual drives yourself will give you the finer level of control in deciding exactly what data needs to be striped. and what needs to be mirrored.' The combination of RAID levels 1 and 0 provide an optimal environment for a database system. called levels. Level 1 offers the best performance. That means that the nice new 200GB disk array that you just bought has now been chopped in half. you will never lose any data. This will allow you to do a full restoration from your last full backup. Most database servers have complex backup systems. there are two different types of backup procedures. With that in mind. and still increase performance at the same time. which is when you spread the data out on more than one disk. and will now only be able to store 100GB of the data that you need to put into your database. with RAID all of the striping and mirroring is configured when the disk array is set up. but don't want to spend a lot of time configuring your database and a bunch of separate disk devices. Commonly. RAID level 1 is disk mirroring. It offers maximum performance. There are a few different types of RAID. all of your data on that device is treated the same way. and make incremental backups at intermediate points between your full backups. with minimal performance penalty.
Backup media
The data that you store in your database is probably important to someone that you work for. To find more detailed information about the different RAID levels. where you have the same piece of data stored on more than one disk. in which you save all of the information in your database at that point in time. the RAID controller takes care of that for you. and mirroring. so once it's configured you get to access the entire array just like it was one huge drive on your system. With RAID you don't have to worry about configuring every detail of the disk access yourself.performance of mirroring is happily paid for by the added recoverability that results from having your data in more than one place. Again. RAID RAID systems are nice for the opposite reason. and most complete fault tolerance of all the fault−tolerant RAID configurations. In general. in which you only save the information that has changed since you made the last backup. if you want the performance and security of having your data mirrored. It gives you the advantages of both striping and mirroring. There are different types of RAID setups. you need double the disk space. and then apply the changes that were made with the remaining incremental backups. up−to−the−minute recovery use a combination of the two methods. any piece of data that is stored on that device will also be both striped and mirrored. It is important to remember that when you use RAID. you will make full backups at regular set intervals. The price you pay for RAID 1+0 is in disk space. Raid level 1+0 is a common choice for a database system. but no recovery features. and full backups. A good way to prevent losing the data in your database is to back it up regularly. With this finer level of control you can sometimes save disk space. This is a great advantage. Incremental backups. no matter what happens. The advantage that we are expecting to gain come from the capability to stripe data. 176
. you will want to take good care of the data to ensure that you never lose any of it. To have all your data stored in two places at the same time. and you will want to choose the one that provides both striping and mirroring of your data. that if you follow their guidelines exactly.

Some common media for database backups are tapes and disks. and then use tape as the media for your full database backups. The data drives the specifications. and recover your data to be used from there. Over the long run. Disk Disk drives are also nice for backing up your data. and less convenient to use. second only to the cost of application development. The downside of tape is that it is slower to write to and read from than disk. As of now DVD is more often used as a means of archiving data. Additionally.
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. if your machine fails. That way. Third. This will protect you from more serious failures and natural disasters that prevent data recovery from any of the drives that that data were originally stored on. but they are not as commonly used. you will not lose the data with it. they may begin to work their way into the mainstream for backing up data. That way. A better idea is to store your incremental backups on disk. In most cases you'll find that high performance disk systems are the single greatest cost in a new database implementation. There are also media such as CD−ROMs and DVDs that can be used for backing up your data. or removable. if you lose the disk drives or the entire machine the database is on. an assessment of the data storage requirements are next in the list of important information to have on hand. in part. Linux System Administrator.Backups should be made on media that is separate. The downside of disk drives for backing up data is that they stay inside your machine when they are not being used. you can load it onto another machine. If you want to back up or restore from tape. we discussed some of the elements of the plan for choosing and installing a Linux database. Disks are becoming more attractive as they get cheaper. and application support. we looked at some classifications of information and the particular data needs and uses for some common functional areas in an organization. and rely on disks for the more common backup operations. The data storage needs are. from your database system. The greatest amount of effort is devoted to developing the requirements that are necessary for meeting the organization's goal that will. Typically. Speed is another reason why you might find it better to use tape for the less frequent backups. be met through the use of a Linux database. but as prices drop and DVD writers become more accessible. independent of the particular RDBMS and the operating system. it is the administrative costs of the database(s) that are the largest−DBA. for the most part. This is a problem if your machine fails. and your only source of backup data is sitting inside it. but tape also has some good characteristics that make it a desirable media for backing up your data. This way you will benefit from the speed and convenience of doing the more frequent backups to the faster disk drives. someone has to physically load it onto the machine and leave it there while the data is copied back onto the disks. and store it in a safe environment. Tape is also nice for backing up your database because you can take it away from your machine.
Summary
In this chapter we examined the primary activities and information that are used in planning and choosing a database system. This information can be used when developing a strategic plan for the organization's data. for example. you will not lose the security of having your full backups on the more stable media and removed from your machine. Disks are very fast to write to and do not need to be loaded onto the machine before they can be used. After addressing the organizational issues. and you have a backup on tape.

it is the disk systems that take the majority of the discussion.
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. and on implementation cost.Finally. RAID systems can have a large impact on database performance. Once again. we looked at the hardware that would be expected to have available for a database system.

a database's performance depends largely on its underlying platform.
Architecture
DBMSs follow a client−server architecture. more immediate tasks. First. all database processing occurs on a server. defining schemas that accord with this model needs no complex logic or analysis of underlying data. the relational model is simple and easy to implement. Why do so many DBMSs follow this standard? Two reasons appear frequently in the literature. that is. the more thoroughly and efficiently a DBMS implements a client−server architecture. Tip Where do more recent developments such as object−oriented databases (OODB) fit into this picture? Unless you must store complex data structures. which carries out that processing in response to requests from clients. must process large volumes of data in real time. A client−server architecture has a number of advantages over a peer−to−peer or dumb−tube−to−mainframe scheme from a database point of view. such as those involved in geographical or geophysical applications. or database operator. • If fully implemented. Therefore. Most frequently. Clearly. let's review a few tried−and−true performance−related maxims. a database administrator.
Overview of Choosing Database Products
This section describes the features and design characteristics that should guide your choice of a Linux DBMS. it's unlikely that you need to turn to OODBMSs. the better a candidate it is for any environment. • It reduces network load.Chapter 7: Choosing a Database Product
This chapter explores several Linux−based DBMSs. In a client−server architecture. For instance. tables related by common fields represent most scenarios as effectively as do more complex structures for representing data. evaluating the suitability of each. client and server run on separate hardware−and even operating system−platforms. many DBMSs provide data and user controls beyond those offered by their operating system platforms. such as handling the intricacies of a GUI (graphical user interface). such as those found in network or hierarchical DBMSs. Let's examine the basic characteristics important to all modern database management systems (DBMS).
Hardware and operating system platforms
As you might expect. • It frees the clients to carry out other. connected only by means of a network.
Relationship modeling and the relational model
A critical factor in evaluating a DBMS for use is the way in which a DBMS represents the relationships between and among items of data. because much of the processing occurs on the server. That is. the relational model can link successfully to most categories of problems.
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. Second. therefore. or must provide tools such as natural−language searching and reporting. it allows DBMSs to handle some of the processing load that might otherwise fall to the operating system.

and SQL3. and network services efficiently. including support for: ♦ SQL agents. Consequently. If a suite you're investigating offers SQL−89 compliance and no more. caching.x kernels can only deal with up to 4GB of RAM. you can feel comfortable that the DBMS you choose will work hand−in−glove with any Linuxlike operating system (OS) it claims to support. or utilities. adding a number of important features to DBMSs. the more you can be sure that you'll need a fast processor to take full advantage of those tools. as clear−cut as are questions relating to operating system platforms. FORTRAN. do not consider it for your environment. and you'll do fine. Three SQL standards need to be considered: SQL−89. and SPARC−based UNIX. RISC−. CPU As with memory. that is. superior I/O and memory management. and then only with some patches that introduce other issues. Pay close attention to what the various DBMSs you're considering suggest as memory requirements. which can make or break a database's efficiency record. Not more capacity. and PL/I. For instance.2. must be viewed as a perfectly natural evolutionary step. count on at least doubling the suggested amounts. UNIX has long dominated the DBMS platform market. Pascal.
SQL standards
SQL standards and their impact on the choice of a database are not. to some flavor of Linux. • SQL−92 goes well beyond its predecessor. but it achieved that status by being so very true−you can never have too much memory. that themselves generate SQL statements ♦ Connections from client to server being managed by SQL agents ♦ A much broader variety of human languages ♦ Advanced data types such as Binary Large Objects (BLOBs) 180
. Read the labels. unfortunately.3. For example. but more speed. DBMSs depend on the operating system's capability to provide disk. Further. SQL−89 implemented checks on referential integrity only as an option.RAM It's a cliché.x and 2. and process management that enables administrators to quickly intervene to correct CPU bottlenecks and gridlock. Because UNIX offers capabilities such as support for many simultaneous client connections. and features such as multithreading and multitasking. major database vendors such as Oracle and Sybase have supported it for years. The porting of DBMSs from these and other vendors to x86−. And the more flashy features a particular DBMS offers. of course. Tip One must. Operating system This one's a relative no−brainer. Then. Even more than other categories of applications. so with processor−more is better. the Linux 2. exercise common sense in this regard. this standard initially offered the ability to invoke SQL commands only from the programming languages: COBOL. Data−intensive applications like those this book discusses make this more a fact of implementation life. • SQL−89 can be viewed as the lowest common denominator of DBMS capabilities. SQL−92.

triggers. without the use of indices. For instance. So. Specifically. powerful tools for a database administrator (DBA). they should not play the primary role in choosing a DBMS for several reasons.Tip Examples of BLOBs include multimedia files such as audio and streaming video. faster disk I/O and a faster DBMS. SQL3. and rules are very useful. your DBMS might include a rule that ensures that the server would not accept a user−entered date such as February 31. has yet to be addressed. cause an action to take place within the database when certain predefined conditions occur. or utilities. among them Oracle8i for Linux. Triggers. a trigger might be initiated by a user deleting a record. by many DBMS vendors. Often. Tip If your environment must organize and track large amounts of object−oriented items.
Operating system−related performance issues
Many DBMSs. in choosing a database application. many DBMSs. Stored procedures have been defined as collections of SQL statements and procedural logic that reside on the DBMS server. They are considered database objects. and even from release to release. triggers. let alone fully implemented. and rules are DBMS terms for what we might call library functions. Another reason is the great difficulty or impossibility of porting stored procedures and triggers from one DBMS to another. What's more. particularly open source products. Raw space is unformatted space. As a result. the new standard. are not fully SQL−92 compliant. and might function by requesting confirmation of the deletion. One reason is that capabilities vary greatly from vendor to vendor. triggers. which adds even more capabilities such as user−defined data types. That standard deals largely in object−oriented extensions to SQL. and even to entire domains. because it doesn't have to call upon the operating system to act as a middleman for input or output. or the capability of a database to accurately match values in key fields across tables and two−phase commit. clients can run these pieces of canned code simply by sending a request to the server.
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. Therefore. Does a downside exist? Indeed. as their name suggests. keep an eye on the SQL3 standard and the Linux DBMSs implementing it. and rules
Stored procedures. Two basic DBMS functions are (a) the DBMS's capability to support and carry out referential integrity efficiently. it does. Ergo. try to determine the degree to which the application meets the SQL−92 standard and the timeframe in which its creators anticipate it will implement SQL3. Even today. can bypass the OS's native file system and go directly to the raw disk. Thus. While it's clear that stored procedures. the database server encounters less I/O overhead. but rather are known only by their size and location. or raw space of the physical disk partition.
Stored procedures. look for a DBMS that supports referential integrity and that can apply it to primary keys as well as to columns. for example. Rules refer to a special type of trigger that verifies data before inserting it into a database. BLOBs have no defined structure that can be interpreted by a database. and (b) the practice of storing data in a way that helps to ensure the recovery of data that may have been in transit at the point of a platform crash.

formatted space. Remember that everything has a price.
Managing connections
DBMS servers manage client connections and allocate resources to them in three ways. So. such as queries. But if your OS permits a database server to allocate resources to its own processes. So. • Linux. no choice or problem exists. and act by breaking up a query into smaller subqueries that execute concurrently on different processors. you're not necessarily gaining anything.
Means of multiprocessing
Many flavors of Linux and other Intel. In evaluating databases and their platforms. RISC. rest assured that your OS has been 182
. there are several drawbacks to this technique: • Often. DBMS servers that typically do this sort of job: • Have been written and compiled specifically for parallel query processing. However your OS reacts to the combination of swap and file system on a single physical drive. When a single physical storage device houses both file system. The three client connection management techniques are: • Process−per−client • Threading • Some combination of per−client and threading Process−per−client This approach. If your OS will not give up to an application server the task of allocating system resources. it's certain that a large amount of raw space given over to swap lessens the amount available to a DBMS's I/O. some flavors of Linux permit no other use of any leftover raw space. disk as swap. that is. That is. like UNIX. gives every database client its own process for the client connection. which is spreading an operating system's processing load across several CPUs. a simple 'tar' won't suffice. if your DBMS server happens to be handling 30 clients at a given moment. but rather how it multiprocesses. and how much of this parallel processing can be controlled by a DBMS server. may present more overhead and certainly more expense. • Therefore require a query manager to oversee the distribution of subqueries and the reassembling of subquery results into a coherent whole that can be presented to a user. or SPARC UNIXs support multiprocessing or parallel processing. when a DBMS uses raw disk.Nonetheless. and raw space that contains swap. can use some raw. or unformatted. as its name suggests. what matters isn't so much that an OS can multiprocess. Only if lightninglike response time is critical in your environment should a database server's capability to carry out parallel processing be a factor in choosing a DBMS. it also requires special utilities to be backed up. in evaluating Linux databases. pay attention to the degree to which and the way in which they manipulate raw disk space. When you evaluate a database candidate for your environment. • As a result. a particular suite's connection management method must be considered. don't accept poorer overall system performance or more difficult backups for database performance that may improve only slightly over what it would have been without the ability to manipulate raw space.

and result in delays in servicing client requests. 2. some DBMSs use a combination of process−per−client and threading. and even the DBMS server. again using the server queue. Because they rely less on OS services. Also. with each client grabbing one or more processes. as do many of the Linux DBMSs discussed later in this chapter. In addition. using as much as 2MB per client. Combining process−per−client and threading In an attempt to provide the best of both worlds. Here's how the listener−initiated processing of a client connection works: 1. and runs them all in the same address space. However. Process−per−client does have definite advantages. leaving other threads languishing in line until the gluttonous one relinquishes the processor. Further. However. Such a scheme can maintain a protected processing environment like that enjoyed by process−per−client. Among Linux databases. 3.
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. as a result. because the thread requires less management. the most significant being the fact that threaded applications don't distribute resources even−handedly. A more formal and more Linux−related definition: a lightweight process that executes more quickly and demands fewer system resources than a 'true' or 'heavyweight' process.presented 30 separate additional processes. like a line in a connect−the−dots game that links data and instructions pertaining to a particular task. Oracle8i stands out in this category. process−per−client gobbles up your resources. this queue can back up. Threading also has its own process scheduler. Oracle for Linux uses a multithreaded agent called a listener. as can happen with so many categories of tasks. Oracle8i for Linux has full multithreading capabilities. process−per−client DBMSs tend also to be RAM gluttons. as individual threads. without having actually to allocate a process for every connection. Tip Earlier versions of Oracle used process−per−client. more interprocess communication. The listener establishes client/server connections by assigning client requests for services to another agent called a dispatcher. Threading can instead monopolize a CPU. The dispatcher sends requests from the client to a server queue. It's easy to see the disadvantages of this technique. process−per−client can be more readily and efficiently managed by multiprocessing operating systems running on multiple CPUs. and starts the response on its way back to the client. Threading Threading views individual client connections. Does threading have any disadvantages? Yes. threaded applications also port more easily. The biggest advantage is that client connections that operate as individual processes reside in their own process address space in memory. Tip Just what is a thread? An informal definition: a path or track through memory. takes place. and thereby receive built−in protection from misbehaving processes that share space. though. A server process takes the message off the queue. First. with its attendant overhead. executes the request inside the database server engine. thereby freeing any application that employs it from reliance on an operating system's process−management mechanisms.

The standards are definable as follows. bundle administration and monitoring tools with itself. • D−level security: A nonsecure system or application • C−level security: Some security provisions.
Administrative and other tools
Think of them as necessary frills. includes: ♦ C1: User log−on required. in the document Trusted Computer System Evaluation Criteria (DOD standard 5200. Tools to look for include those that expedite: • Backing up and restoring a database • Carrying out user administration • Fine−tuning and maintaining DBMS security • Fine−tuning DBMS performance Even more attractive is a database suite of bundled tools that enable you to monitor the database's cache usage. a subsidiary organization of the National Security Agency. and so on. and processor usage. Note All of the Linux DBMSs covered in detail in this book−MySQL. age passwords. and as is too often the case in the real world. disk access efficiency. Such databases are more expensive and perform more poorly. If. group IDs also permitted ♦ C2: Individual log−on with password required. on the other hand. connection management becomes a more important question in evaluating database candidates. Any DBMS that you're considering should. Oracle8i and PostgreSQL offer at least some of the monitoring tools just mentioned. But as you probably have guessed. you're lucky enough to have CPU and RAM to burn. Therefore. audit mechanisms available • B and A levels: Provide mandatory control with access based on standard Department of Defense clearances Most UNIXlike operating systems offer C1 security by default. If. for example. and Oracle8i−have multithreading capabilities built in. PostgreSQL. ideally.
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. you must implement in a limited setting. detect intruders. there's a price for this additional security. the Linux DBMSs we're examining either do or can closely monitor user activity.
Government Security Standards Government and other security standards are set forth by the National Computer Security Council.28−STD.Evaluating client connection−management methods Correlating candidate DBMSs' client connection−management techniques with the suitability of the suite to your environment must begin with an overview of system resources. December 1985). Tip Of the Linux DBMSs covered in detail in this book. and can be upgraded to C2 without undue effort. client connection−management need not play a significant role in your DBMS selection process. because they demand so many additional system resources to be capable of accomplishing the additional security they offer.

and MySQL 3. or object−oriented). and integrity constraints. table.
Capability to interface
You should consider whether. have the capability to save query results as flat ASCII files whose fields are delimited only by white space.1. • Relational: based on a model developed by E. Also called multirelational model. and row/record levels. the DBMS you're evaluating can interface with application programming interfaces (APIs) and with executable libraries for such applications as data communications.
DBMS Models Here are brief definitions of the three most significant DBMS models.Security techniques
All Linux DBMSs worth considering offer security at the database.23.. a record type called inventory relating to both a customer and a product record type. or to specific application characteristics that best fulfill the criteria implied in the question should be examined. Such databases can prevent at all these levels: • Damage to data due to collisions or overlapping of modification attempts • Unauthorized access • Unauthorized modification However. RDBMSs enable the definition of data structures.F. and fields. and to be interpreted only using methods similar to those of object−oriented programming. Even more useful would be the capability to export directly in Access or other Microsoft or Windows−compatible formats.
Overall performance
In evaluating database candidates. and drag−and−drop capabilities. For instance. for example. graphics. storage and retrieval operations. OODBMs preserve relationships between 185
. you might ask the MySQL Project. • Network: model in which each record type can have multiple parent relationships. and data and relations between data organized by tables.
General design and performance questions
Finally a number of general questions that pertain to database functionality and the overall DBMS model (relational. and how easily. PostgreSQL 7. records. column/field. network. compare their performance. this doesn't make these DBMSs hack−resistant.2. Note Check out new releases of these products−recently released or about to be released as of this writing−Oracle9i. PostgreSQL Inc. at a minimum. Should your users need to interweave data derived from a Linux database with tools such as Microsoft Access or PowerPoint. RDBMSs use key fields to enable automatically indexed searches for specific values of that field. the selected database must. Codd. Request performance statistics from vendors for the same task. Should you need to at least approach that ephemeral goal. and Oracle Corporation for mean response time to a simple query when ten or more clients connect to a server. • Object−oriented: model that requires data to be stored as objects. consider a DBMS that complies with such government security standards as C2 and B1.

be what your DBMS tracks? If so. your environment would be best served by a DBMS that adheres to the network or multi−relational model. Number of simultaneous transactions and user sessions Do you anticipate numerous users accessing your databases simultaneously? Will each user perform a multitude of modifications to those databases? If so.similar objects. the relational DBMS model will most likely best serve your needs. MySQL provides such capabilities only through add−on tools. Although all three rely heavily on the relational model. Of the three Linux DBMSs covered in detail in this book. you'll need an application that can work according to the object−oriented model. as well as references between objects. Such suites handle schema changes more readily than network or object−oriented databases. do you anticipate that the schema of this database will be relatively unchanging? If so. your needs will be best met by a DBMS that adheres to the relational model. you have several options. such as the capability to support very large databases being accessed by multiple simultaneous users in a client−server environment.
Fields If a Linux DBMS has multiple occurrences of a few data items in slightly different contexts.
Choosing a DBMS
When choosing a DBMS. your needs may be best served by a DBMS that follows the network model. OODBMs often provide queries that execute more quickly because of a lack of need for joins due to capability to retrieve an object without a search by means of its object ID.
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. Percentage of multimedia or other BLOB data Will multimedia data. they also offer some features that are more typically associated with the network model. Size of database Will your database have to store and manipulate a very large number of records? Also. PostgreSQL and Oracle8i offer significant object−oriented capabilities. the more it needs to rely on the classic relational model for databases. Frequency of schema modification If your database design must be changed frequently. Speed of updates The more critical response time is to your DBMS. such as video and sound.

as well as databases that contain BLOBs • Adherence to the SQL standard • Availability of libraries and client programs • Multithreaded. control of multiple databases. the ways in which OFA attempts to accomplish these admirable goals may themselves create at best overhead and at worst problems. The site emphasizes these points about the product: • Capability to handle very large bodies of data. reliable databases that require little maintenance. OFA also attempts to minimize fragmentation in both data and schema storage. Oracle Corporation points to these features to demonstrate that Oracle8i for Linux is an enterprise−ready product: • A database development environment • An applications development environment • Open Database Connectivity (ODBC) libraries • Support for multiprocessing • Support for Apache. MySQL remains very much a work in progress. the world's most widely used Web−server application To offer these and other features. as well as to organize software and data in such a way as to avoid bottlenecks and poor performance.com lists what this DBMS's creators consider important in a database system. MySQL offers production capabilities. can be obtained for little to no cost. including such as free upgrades. Specifically. client−server architecture • Multiuser nature Its developers created and tested MySQL in an environment that included: • A significant percentage of tables containing more than 7 million records • Approximately 10. Also like its open source peers. Consider these points made in various areas of Oracle8i documentation.mysql.
Oracle
Among other things. Specifically. and as the figures above state. OFA attempts to facilitate the administration of data and schema growth. Oracle Corporation intends its DBMS Oracle8i to compete with such market staples as the DBMSs that run under Windows NT.000 tables • More than 40 databases • At least 100GB of data Like all open source products. Even better. and routine administrative task backups.MySQL
The MySQL Web site at www. 187
. Oracle Corporation addressed both concerns by the original port of its DBMS to Linux and by a commitment to an ongoing enhancement of the ported product and to full support from Oracle Corporation. However. Oracle Corporation considers OFA to be a set of configuration guidelines that permit the creation of fast. Oracle8i relies largely upon a design paradigm called Optimal Flexible Architecture (OFA). again like its open source companions. One of Oracle's senior Linux development managers has pointed out that the Linux community itself has expressed the need for broadly relevant applications and the user community at large has been skeptical about Linux because of the lack of a variety of applications from which to choose. the price is right. MySQL.

including B−Tree and hash • ODBC drivers are available • Online backup is supported • Online documentation is available • Online recovery is available • Parallel querying is supported • Read−only databases are available • Row−level locking is available • Shared SQL cache • Several operating systems supported. each point seems completely sound. • Spreading Oracle8i databases and software across more than one drive minimizes the impact of drive failures on those databases and software. In its developers' own admission. including FreeBSD. But in the real world. including C. and Solaris x86 • Several programming languages supported. the reliance on RAID might introduce expense and administrative complexity that other means of protecting the integrity of the DBMS might not. For example. to small environments or small. a large. On paper.• Hardware costs should be minimized only when doing so does not conflict with operational considerations. the open source incarnation of Ingres.
PostgreSQL
In a very real sense. each may introduce complications as thorny as the circumstances they intend to preclude. PostgreSQL. Java. heavily subdivided database might result in a file subsystem that proliferates to the point of gobbling up too large a percentage of the OS's inodes. Python. Oracle8i's admirable attention to processing efficiency and database integrity make it somewhat ill−suited. PostgreSQL combines the strengths of both MySQL and Oracle8i for Linux. minor) drawbacks of either. In a nutshell. evolved in an academic environment. and Tcl
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. Perl 5. Linux SPARC. Perl 4. Linux Alpha.' As a result. Solaris SPARC. Or. NetBSD. SGI Irix 5. without the (admittedly. its growth since 1995 has emphasized adding or improving: • Commercial−style features such as telephone support • SQL functionality that was missing • Support for complex data types • Support for complex queries • Transaction support • Locking • SQL conformance The following list of some of PostgreSQL's features demonstrates the DBMS's part−commercial. • Multicolumn indexes are available • Multiple index types are available. Linux x86. PostgreSQL 'had not been exposed to the full spectrum of real−world queries. part−open source persona. simple collections of data.3. despite its many strengths. in many environments. • Oracle8i's practice of separating categories of files into independent directory subtrees minimizes the extent to which files in one category can be affected by operations on files in other categories. C++.

Weaknesses of commercial products It's said that in real estate the three most important criteria are location. Many also support features critical to e−business applications. SQL−92. and COBOL • Support for the standards ANSI.
Commercial products
More commercial Linux DBMSs than you might imagine exist. or if it offers that code only at additional cost. you must consider commercial database management systems.
Strengths of commercial products Most of the products here offer sophisticated management tools such as the capability to administer remotely via the Internet. For these reasons. In addition. you may want to forgo commercial database management systems. stored triggers and procedures. that might be paraphrased as cost. a product of Software AG of Frankfurt. multimedia data. referential integrity. and updatable join views. and cost. ADABAS/D has been ported to Linux since 1997.
ADABAS/D
Adabas/D. C++. None of the commercial Linux DBMSs we review here is inexpensive. provides a professional database system that fully implements the relational model by supporting domains. In business. these products make available GUI−based development toolkits and environments that surpass the capabilities of similar open source tools. Sample commercial products Now. and location. If yours is a small environment with relatively simple data management requirements. let's look at 12 commercial Linux DBMSs. This section reviews the pros and cons not only of this category. location. and if your environment requires object−oriented or network DBMS features. primary keys. and streaming. but also of individual representatives of it. including the capability to handle BLOBs.Candidates
This section discusses the strengths and weaknesses of commercial Linux database suites and open source Linux DBMSs. cost. Among its features of primary interest to business environments are: • Capability to increase data space areas without shutdowns or reorganization • Low cost compared to other commercial alternatives • Silent operation without permanent supervision • Balanced B* trees to optimize storage allocation • Scalability on multiprocessor systems • Multithreaded architecture • Record−level locking • Support for C. and OFA • ODBC support 189
. Germany. Note A DBMS belongs in the commercial category if it does not make source code available.

demonstration. an integration of Internet and intranet HTML documents with the DBMS's file system • Supported operating systems include SUN Solaris 2. which can be used in an intranet or via the Internet. a built−in scripting language designed for enterprise−class transaction processing • Caché SQL Server. ActiveX. including support for inheritance and multiple inheritance. to automate the creation of Microsoft Visual Basic forms and to link Cach database objects with these VB forms See www. administrative interface that can be run from any Java−enabled Web browser • Increased table/column limits • Lightweight Directory Access Protocol (LDAP) support • OLE DB Container Support • Replication capability for BLOBs • Support for JDBC and SQLJ • Stored procedures • Unicode support Tip DB2 Personal Developer's Edition can be downloaded at no charge. and relies on both a transactional paradigm and the multidimensional DBMS model. testing. includes these significant features.• JDBC support • Includes a Perl Version 5.softwareag. the Intel port of the company's longstanding DBMS. a GUI−based development environment • Caché WebLink. and which permits remote database installation and server configuration • GUI front−end for queries on all supported platforms • WebDB. • A multimedia.5 or higher. a networking technology that dynamically distributes the database across the network in response to processing demands • Caché Object Server that permits direct use of Caché Objects by Java. and support of popular object languages and technologies including Java. but may only be used only for the evaluation. and Linux See www.
Caché
Caché calls itself a 'postrelational' database.com for more information. and C++ language processors and development tools • Caché ObjectScript. Although there is no time 190
. and C++ • Visual Caché. that provides access to databases by either SQL or ODBC • Caché Studio.4 tool • Includes a Tcl/TK interface • Remote Control. Its significant components include: • Caché Distributed Cache Protocol (DCP). ActiveX.com/cache for more information.e−dbms.
DB2 Universal Database for Linux
IBM's DB2 Universal Database for Linux. that provides connectivity between Caché and Web servers for Web−based transaction processing applications • Object−Oriented functionality. SCO UnixWare. Web−ready relational DBMS • A performance monitor • A Perl driver for the Perl Database Interface • Connection enhancements such as connection pooling • DB2 Control Center. a graphical database administration tool. and development of application programs. support for multimedia and application−specific data.

client−server. SuSE Linux. 30−day evaluations of all its Linux suites.com/software/data/db2/linux for more information.limit on its evaluation. including full integrity constraint checking built into the server • In−memory table caching • Multicolumn B−tree indexing 191
. it cannot be used in a production environment. features a fast RDBMS with a small footprint • Empress Web Database Toolkit for the creation of interactive.ibm. and bulk Tip Empress Software offers free.' FrontBase. and multiserver architectures across heterogeneous networks • Fully integrated report writer to produce custom−formatted reports • Interactive. and User−Defined Procedures • Fully distributed. on−the−fly encryption • Built−in mirroring ability • Conservation of storage by using the UTF−8 standard for data representation • Exclusive use of Unicode 2. • Capability to back up live databases • Access privileges at the record level • Block mode. See www. a compact SQL−database engine. float.
FrontBase
Billed on its Web site as 'the only enterprise−level relational database server with zero−administration. YellowDog Linux.empress.com/ for more information. which has provided database products for Linux since 1995. and redefine attributes to a table without unloading and reloading data • An extended transaction mechanism that allows multiple transactions to be named and nested within each other • ANSI SQL database • Automatic two−phase commit to help ensure data integrity during transactions • Data−transfer and data−loading utilities • Extended objectlike capabilities such as Persistent Stored Modules.0 for all character data • Full compliance with the SQL−92 standard. User−Defined Functions. embedded SQL • Kernel−level C and FORTRAN interfaces to the database engine • Kernel−level X Window System interface access for more efficient GUI−based operations • Recovery utilities to restore databases in the event of a major failure • Referential constraints and range checks built in to the data dictionary • Strong integrity and recovery features • Support for numerous universal data types including text. drop. data−driven Web pages At the core of each of these Toolkits lies the Empress RDBMS. and Solaris. offers three products: • Empress E−Commerce Database Toolkit for development and deployment of e−commerce applications • Empress Embedded Database Toolkit for developers of embedded systems. Empress RDBMS has these significant features: • Capability to add. offers these significant features. See www. which is available for Linux platforms such as Red Hat Linux.
Empress Suites for Linux
Empress Software.

locking procedures. or database levels • The capability to restore tables or even an entire database. Informix Corporation emphasizes Informix SE's performance. Among the suite's specific features that support these claims are: • A variety of indexing options that can involve indexes covering one to eight fields. transaction logging. and ease of administration. and isolation levels • Meets SQL−92 entry−level requirements • Native language support based upon the X/Open XPG3 specification • No need for OS kernel modification in order to provide such features as shared memory or the use of raw devices • Permits a maximum character field size of 32. based on the capability to collect and calculate statistics about specific data distributions during nonpeak processing hours in order to provide a means to avoid bottlenecks during heavy loads • The capability to lock at the row. inserting. on−the−fly encryption of client−server communications • Support for gigabyte BLOBs • Support for gigabyte character−type field values • Support for streaming QuickTime content • Support for terabyte databases • Tool to migrate MySQL databases See www. standards adherence. and table privileges that allow such tasks as modifying. data consistency.com for more information.frontbase.767 columns per table • Permits a maximum of 1 billion rows per table • Permits a maximum record length of 32.
Informix SE
On its Web site. client−server capabilities.511 bytes • Permits a maximum key size of 120 bytes • Permits a maximum of 32. table. such as an SQL SELECT FOR UPDATE request's precluding other SELECT FOR UPDATE transactions' locking records already being updated • Support for entity integrity by enforcing acceptable data values for fields • Support for integrity constraints. and triggers • Support for referential integrity. as well as B+ tree indexing options that include unique and clustered indexes • Built−in client−server connectivity by means of libraries that preclude the need for any additional networking products • Maintenance of data consistency by means of audit trails.• Reliance on sockets for client−server communication.767 bytes • Reliance on the native Linux file system for simplification and speed of data storage and retrieval • Supplies utilities that migrate Informix SE data in ASCII format to other Informix databases • Support for a number of levels of read−only isolation control. and deleting data
192
. for example by ensuring that information about an entry in a master table remains intact as long as corresponding information still exists in a detail table • The capability to automatically determine the fastest way to retrieve data from a table. in the event of a system failure. based on audit trails • Two levels of access privileges to help to ensure database security: database privileges that permit creating tables and indices. stored procedures. thereby providing support for a variety of client platforms • Remote management ability from any Web browser • Stored procedures • Streaming.

Finally. always reports such resources to be available. which it calls the Open Source Database. the Ingres II system−requirement checking utility. See www. or Ingres' Visual DBA tool. through which an InterBase server can be created and managed. we must still consider InterBase a commercial or quasi−commercial product. and was released as a production tool for Linux and Solaris only in July 2000. includes features such as: • IngPerl.0 or earlier. As a result. such as enhanced security. or with which you can create and administer databases on that server • A Replicator that facilitates replication and synchronization between multiple InterBase databases that have similar structure • A services API that enables you to write applications that monitor and control InterBase servers and databases. whether or not they are in fact available • Ingres II cannot run under Red Hat Linux 5. primarily to application developers who have facility with GNU development tools and Apache Web Server. the most significant of which are: • Syscheck. this beta has several known bugs that are as yet unresolved. because it offers features such as: • An integrated graphical user interface called IBConsole. the beta of Ingres II does not include other features offered by the commercial version of Ingres II. that is. for the foreseeable future at least. possible tasks can include: ♦ Backup and restore ♦ Shutdown and restart ♦ Garbage collection 193
. the release has not yet occurred. InterBase 6 deserves consideration as a Linux enterprise DBMS.
InterBase
Tip
Despite Inprise Corporation's January 2000 announcement that it planned to release InterBase 6. because of incompatibility problems between the glibc library versions offered by the OS and required by the DBMS. in true open source form. However.informix. Ingres database access by means of Perl scripts • Interfaces for C • Internet−publishing capabilities • Row−level locking • Support for BLOBs • Variable page size • An embedded SQL precompiler • C2 security auditing • Query and reporting tools • Terminal monitors However.htm for more information. object management tools. that tries to determine whether the machine on which Ingres II is running has sufficient resources.com/products/ingres. Ingres II for Linux will be of interest. that beta version. Regardless of such sticky points. available for free download. however.com for more information.cai. InterBase 6 remained in beta release as late as May 2000.See www.
Ingres II
Ingres II for Linux remains available only as a beta release. tools for establishing security beyond C2. that is. networking utilities.

supports complex object definitions without the need to decompile those objects in order to modify them • A network communication layer that supports direct communications−that is. and object references See www. NUMERIC and DECIMAL data types with 10 to 18 digits of precision−stored as 64−bit integers ♦ Support for read−only databases ♦ Support for SQL−delimited identifiers. have been made available to the Linux community. and for Asian languages through multibyte character sets such as Chinese and Japanese • No practical limits on database size other than those imposed by the hardware and operating system platforms • Security features that include user accounts and object privilege levels • Support for indexing individual words.com for more information.
Oracle8i for Linux
Oracle Corporation considers Linux one of the fastest growing operating system platforms in the enterprise environment. for database object names that are delimited by double quotes ♦ The capability to back up and restore a database to or from multiple files ♦ The concept of dialects that enable users to move ahead with new features.kesoftware.com for more information. TIME. as well as complex data types such as dates and times • Support for object−oriented database structures that offer such features as text attributes. such as delimited identifiers. and TIMESTAMP ♦ Support for Delphi 5 ♦ Support for large exact numerics−that is. the Oracle8 and Oracle8i DBMSs. and TIMESTAMP data types. nested tables.interbase. as well as Oracle DBMS suite components such as Application Server. Jserver. offers an engine that includes such features as: • A nested relational database model that. including in the latter: ♦ API calls that will be replaced in future versions of the product ♦ Pending database shutdown ♦ SQL expressions that produce different results in different InterBase versions ♦ SQL statements with no effect ♦ New data types SQL DATE.
194
. multivalued fields. and WebDB. a DBMS suite that follows the object−oriented model. remote function calls−as well as both TCP/IP−based network communications and serial line connections • An object−based method of indexing that results in unusually quick retrievals • Fully integrated support for European languages through 8−bit extended ASCII.
KE Texpress
Texpress. and the SQL DATE. and field values. TIME. Consequently. large exact numerics. that is. and cites the OS's millions of users as the reason for its commitment to Oracle on Linux. in turn. modifying. numbers. that are incompatible with older versions of InterBase ♦ The new EXTRACT() function to retrieve date and time information See www.♦ Scanning for invalid data structures ♦ Creating. and removing user entries in the security database ♦ Managing software activation certificates ♦ Improved warnings regarding status of current transactions and of SQL statements.

195
.000 fields • Tables stored as indices. row−level locking in data pages. Sybase Corporation's entry in the commercial Linux DBMS derby.sybase. BFILE. so as to expedite such modifications • Clustered indices that help ensure fast retrieval and updating • Database engine internal parallelism. whose job it is to prevent runaway queries and their system resource gluttony • An asynchronous prefetch operation that helps maximize query speed • The capability to carry out index modification under nontransactional locks.com for more information. and object views • Tables and indices that can extend across partitions • Tables of up to 1.com for more information. and the capability to disable a user account if the attempt to connect to it involves three invalid password entries • Improvements to parallel processing through commands such as CREATE INDEX and CREATE TABLE AS SELECT • Support for object−oriented and relational DBMS features such as nested tables. and transaction−duration locks on both data and index pages See www. offers many attractive features. as well as a larger maximum size for the traditional data type VARCHAR. including parallel query execution and parallel sorts • Fully multithreaded architecture • Precluding the storing of duplicate values for keys in both disk and memory • Storing all statistics data in catalog tables that can be accessed directly by users to whom those statistics might be useful • Support for block I/O as a means of improving performance by reducing actual. whose value can now reach 4.000 bytes • Updatable views that can employ triggers based on the INSTEAD OF clause See www.This commitment to Linux as an enterprise platform is reflected by the features that are new in Oracle8i. including setting time limits to or keeping histories of passwords. and CLOB. including: • Improved security. VARRAYs. in B • Treive format • The new data types BLOB. that is. physical I/O • Support for table partitioning in order to provide parallel processing • Support for up to 31 fields in an index • Task prioritization to attempt to ensure optimum response times • Task prioritizing that can provide more system resources to high−priority transactions • Three types of locking models: page locking on the data page.oracle. including: • A Logical Memory Manager (LMM) with which you can assign database objects directly to named caches • A Logical Process Manager (LPM) that allows you to assign CPU resources to individual applications • A tool known as a Resource Governor.
Sybase Adaptive Server Enterprise
Adaptive Server Enterprise (ASE) for Linux.

6 million terabytes. However. easy loading. versatile suite.
CodeBase for Linux
CodeBase 6. configuration.com
Open source products
As you might imagine. that is. Weaknesses of open source products No open source DBMS that we reviewed is anything less than a fully functional. to be used to greatest benefit. All of the DBMSs discussed here can hold their own in any comparison with similarly structured commercial products. If your environment requires quick.
Strengths of open source products The greatest strength of open source database management systems is their price. This section discusses suites that are representative of the available open source software. In addition. few of these products offer more than minimal management tools. All can be freely downloaded.854.775.036. open source Linux DBMSs present the same advantages as do all open source products: functionality and reliability at little to no cost. All offer complete source code at no additional cost. many DBMSs available for Linux are themselves open source software. and deletes • Exposes its low−level API to provide the ability to customize applications • Permits the creation of individual tables with a maximum size of 8.Unify DataServer
Release 7 of Unify DataServer for Linux adds features such as the following to those that one would expect from a basic relational DBMS: • An industry−standard ODBC interface • Backup verification • Enhanced ANSI SQL standard compliance • Enhanced stored procedures and triggers • Support for backup files larger than 2GB • Support for B−tree and hash indices greater than 2GB Web site: www. or such features as remote DBMS management capabilities. Sample open source products This section summarizes five open source Linux DBMSs. When compared to the licensing and other costs of suites such as those from Oracle or Sybase.808 bytes • Places no limit on the number of tables per database 196
. open source Linux databases may not be for you.372. each open source DBMS we examined requires significant. 9. if not intimate.223. thereby providing the opportunity to customize the suites.unify. and management of a DBMS. knowledge of C and Linux. edits. an xBase −compatible database engine for C or C++ programmers. Note A DBMS belongs in the open source category if it makes the source code for the suite available at no additional cost. has these significant features: • Enables the query of millions of records in a second • Can perform bulk appends.

MiniSQL was designed with these criteria in mind: to comply more fully with the ANSI SQL−92 specification. in the capability to accommodate high−end applications that involve as many as 1 million records.• Provides full multiuser record locking • Supports multithreaded standalone or client−server applications • Supports the xBase file standard. in db.
MiniSQL/mSQL
MiniSQL 3.215 records to be stored as a single file. and that is compatible with any ANSI C−compliant compiler. retains and satisfies its progenitor's design goal: to provide high−speed access to small data sets. pointer−based navigation.777.0. thereby providing compatibility with FoxPro. to provide better performance for simple operations. the capability to define multiple indices for every table. and efficient caching • Support for features of both the relational and network database models • Timestamp support • Transaction logging See www. 2001.967.040 records per database • Requires only about 200K of RAM.294. reentrant code architecture that provides support for multithreaded applications and numerous multiple simultaneous user sessions • Enables up to 16.sequiter.linux parlance • Autorecovery from transaction logs • Compound keys • Limits the number of fields in a record only by the maximum record size • Optional support for read. however.0. management of user groups. you can now have your database on your hand−held computer. Specifically.com/products for more information. for an allowable maximum of 4. dBASE and Clipper data files See www. MiniSQL seeks to fulfill these criteria with: • W3−mSQL 2. or about 40K if data access is read−only • Support for B−Tree indices. Centura's most significant characteristics in accomplishing that feat are: • A C API that includes a library of more than 150 functions. the most recent incarnation of the mSQL open source DBMS which became available on February 15. and creation of authorized users through a 197
. Mini SQL goes well beyond mSQL. such as GNU C • A data definition language (DDL) that is largely based on the C programming language • A thread−safe. MiniSQL was programmed to accomplish this latter goal through better handling of complex queries and large data sets.com/dblinux for more information. and the capability to include as many as ten fields in any such index • Enhancements to authentication of users connecting across the Internet.
db. Yes. for example. write. and to provide rapid access to large databases and complex operations. including configuration. definition of secure areas.linux
Centura's db.centurasoft.linux stands alone among all the DBMSs we reviewed as a suite that enables developers to build applications for e−business and information appliances. a second−generation Web interface package that provides a complete scripting language and full access to the mSQL API within an HTML tag • Enhanced indexing that includes. and exclusive locks • Permits records of up to 32K in size • Provides for up to 256 record types per database. that is. as a table or record type.

several floating−point and fixed−decimal−point types.
MySQL
MySQL's most important design goals were ease of use. more than 10. by requiring that once software has been licensed as GPL. which permits an unrestricted amount of data to be inserted into a field by using an overflow buffer scheme to hold data beyond the specified size of the field • The introduction of candidate rows abstraction to expedite query processing. as one reviewer has termed it.' Tip A Berkeley−style license allows anyone to use source code in any way.hughes. But if you have these skills. and more than 40 databases. as long as that use is accompanied by an appropriate copyright notice. and autonumber. and the like. which operates under a University of California at Berkeley−style rather than a GPL license.000 tables. Tip It's anticipated that upcoming releases of MiniSQL will support more data types.com. MySQL has been developed and tested in an environment that presents 500 tables with more than 7 million rows. two−dimensional geometric−shape types that can represent polygons. which have been defined in the most recent SQL standards. is nonetheless.graphical interface accessed by means of a Web browser • Storing indices in a series of B−tree structures that are mapped into the virtual memory address space of the mSQL server process. More than any of its open source or commercial peers. any subsequent distributed versions must also be GPL. deceptively simple DBMS can handle very large databases at least an order of magnitude faster than can many commercial database management systems. which are most often found in large commercial DBMSs. The GPL license goes further in attempting to ensure the right always to have access to GPL source code.
Among the suite's most attractive characteristics are: • A GUI−based administrative tool • A permissions syntax that resembles Linux file access permissions • A reasonable degree of compliance to the SQL−92 standard • An impressive set of data types for fields.
PostgreSQL
PostgreSQL. think of this technique as an analog to the prediction and predication used by CPUs to 'guess' which data will be required next and to retrieve that data in anticipation of its being needed See www. circles. time interval. and speed. MySQL requires a comfortable familiarity with the Linux command−line environment and with manipulating C source code. candidate rows abstraction enables a module performing a query request to also request matching rows as well as the physically next row from tables that have been identified as candidates that might fulfill selection criteria specified in the query.tcx. about 100GB of overall data. a handful of integer sizes. both fixed− and variable−length strings. thereby helping to ensure extremely fast retrieval of key data • Support for a variable−length character data type. including all standard SQL data types. multidimensional array types. more esoteric data types such as Boolean. 'about as open as open source gets.au/ for more information. The MySQL Web site offers benchmark test results that demonstrate that this compact. Furthermore. you may need look no further for a DBMS than this Goliath in David's clothing of a database. and. as well as data types such as BLOB. since 1996. 198
. such as DATE/TIME and CURRENCY. See www. robustness.se/ for more information.

Debian. make it eminently suited to a variety of environments as well as easily obtained. This suite's intriguing set of data types. FreeBSD. and. This technique therefore reduces the size of routing tables. GUI−based administrative tool pg_access.1MB RAM for the server daemon.in an admirable thoroughness. and so forth 199
. such as the time interval data type • Support for more sophisticated query constructs such as subselects • Support for transaction commit and rollback • Support. and .tgz • Its being bundled with several popular Linux distributions.postgresql. Commercial product Our recommendation for a commercial Linux DBMS is Oracle8i. Our recommendation for an open source Linux DBMS is PostgreSQL. and its handy distribution formats and bundling options. on the server side. and most major UNIX variants. including Red Hat's • Its parsimonious use of system resources. on the client side. using only about 1. including.
Recommendations
If this were a multimedia publication. Rather than advertise a separate route for each destination in a group. which store network and internetwork routes. a router that uses CIDR can use what's called a supernet address to advertise a single aggregate route that represents all intended destinations. albeit support that results in rather slow processing. installed. the internal address books of routers. capability to incorporate clients from the Microsoft side of the fence. which is remarkable among open source database management systems. even data types specifically intended for IP addresses and Classless Interdomain Routing or CIDR blocks Tip CIDR attempts simultaneously to represent multiple IP addresses. 98. We chose this product because it is among the most fully featured DBMSs in either the commercial or the open source categories. That commitment must surely help guarantee the continued high quality of this product. investigate for each candidate. trigger. • Its availability in the big three of Linux distribution formats: Red Hat's RPM. Linux. for example. and configured. these factors. in comparison to the approximately 950KB needed by a common Linux shell such as bash • SQL functions and algebraic operators that handle PostgreSQL's more esoteric data types. for BLOBs • The combination of operating system platforms with which it can work. all these as well as Windows 95.
Open source product
Summary
When choosing a DBMS. commendably miserly use of system resources. we've arrived at a single recommendation for Outstanding DBMS in both the commercial and open source categories. • Adherence to SQL standards • Administrative tools • Architecture • Handling of stored procedures.org for more information. because of Oracle Corporation's commitment to Linux. as importantly. in as much detail as possible and practical. we would insert a drum roll at this point. Taking into account all the evaluative premises we've discussed in this chapter. and NT • The relative simplicity of its installation See www. and.

Table 8−1 describes MySQL's component programs. tables.Chapter 8: Installation
This chapter discusses installing Linux−based databases. either as SQL statements or as tab−separated text mysqlimport Utility that imports text into databases by means of the MySQL statement LOAD DATA INFILE mysqlshow Utility that displays information about databases. optimize. with which you can obtain a full list of a particular command's other options. Tip Individual MySQL programs each take different options. or repair MySQL tables mysql_install_db Script that creates MySQL grant tables and the default privileges those hold mysqlaccess Script that checks access privileges.
Table 8−1: MySQL Programs Purpose Creates a binary release of a compiled MySQL. which could then. highlighting the most significant tasks involved with loading each of MySQL. for instance. That ease is reflected in the installation process for the server.
MySQL
As the MySQL Project states on its Web site. and Table 8−2 outlines MySQL's environment variables. display information on. an important goal of the open source database is ease of use. and PostgreSQL. default: $HOME/mysql_history Default MySQL password Default TCP/IP port number Default Linux socket used for connections to local host Directory where MySQL's temporary tables and files reside 202 Program make_binary_release
. Oracle8i. and even indices replace Utility used by msql2mysql safe_mysqld Script that starts the mysqld daemon with safety features such as the capability to restart the server or to log runtime information Table 8−2: MySQL Environment Variables Variable MYSQL_DEBUG MYSQL_HISTFILE MYSQL_PWD MYSQL_TCP_PORT MYSQL_UNIX_PORT TMPDIR Contains Options available for debugging MySQL Name of file which stores client command history. each also offers the option help. matching specific host/user/database combinations mysqladmin Administrative utility that handles such tasks as creating or dropping databases mysqld MySQL server daemon mysqldump Utility that dumps a MySQL database to a file. be sent by ftp to other locations msql2mysql Shell script that converts mSQL programs to MySQL myisamchk Utility to check. However. fields.

A socket is a mechanism. in an effort to preclude a child thread's interfering with either its parent or its siblings. every data communications or communications−related application has a unique port number associated with it. a situation arises that is unlike that produced when a process creates a new process.
Requirements and decisions
Installing MySQL begins by reviewing its requirements and then deciding which of its forms to load. As a result. and returns an integer value which acts as a file descriptor for that point or socket. MySQL has been reported to compile successfully on these operating system/thread package combinations: • AIX 4. A TCP/IP port is also a channel or channel end point. 3.x with native threads • FreeBSD 2. have specific default ports. introducing the further possibility of their interfering with one another. which originated in Berkeley UNIX.
Tip If all you need to do is to compile MySQL client code. In effect. that address consists of a TCP/IP port number and the local host's network address. are similar to Linux processes. sockets act as conduits between standard I/O and networked communications facilities. as it almost invariably does. it is possible for parent and child threads to execute concurrently. logically enough. you can forgo the POSIX threads and just ensure the C++ compiler. socket().x with native threads • BSDI 2. Some TCP/IP application−level protocols. or child processes. but can also be configured to use other ports. Tip Threads. and 4. uses port numbers to distinguish between different channels on the same network interface on the same computer. To understand POSIX threads. but are not processes themselves. In the latter case. one must understand the idea of thread synchronization. begin execution at the same point as their creators or parents. Operating system While it has been written to and tested under Solaris from Sun Microsystems and Red Hat Linux.x with the included MIT−pthreads package • BSDI 3. MySQL should compile and run under any operating system that includes functioning POSIX threads and a C++ compiler. such as telnet or HTTP. but take different paths through system resources. However. Sockets are established and maintained by the operating system library function called. When a thread creates a new thread. as they occur in this and other data communications contexts. the POSIX thread standard was developed to provide two−thread synchronization techniques.x with the included MIT−pthreads package 203
. The file /etc/services defines these port numbers.1. which creates a communications end point (either origin or destination as the case may be). Each socket receives a socket address. Therefore. for creating a virtual connection between processes.0.Sockets and Ports Sockets and ports. also sometimes called lightweight processes. TCP/IP running on Ethernet media. the new processes. refer not to physical devices but to virtual devices.

Possible suffixes are: ♦ alpha: The release contains large amounts of new code that hasn't been fully tested. MySQL evolves constantly.0. Furthermore. Ordinarily. but that holds no known bugs. source code is always the ultimate manual. a gamma release has existed and been played with and in general banged on for quite some time. Source (to compile) or binary (executable to run) Your second decision regarding which MySQL format to load is closely related to the first.3/1. describes file format. ♦ no suffix: The release has been run for an appreciable time at different sites under different operating system/hardware combinations.5 or higher with native threads MySQL version As is the case with open source software in general. • The first number. citing our example and assuming that release level 37 represents the stable branch. we review the MySQL naming scheme here. should he or she carry out an upgrade of MySQL. or 21 in our example. MySQL release numbers consist of three integers and a suffix. existing tables must be converted to the new format. or if you are porting it to a system for which there is no binary distribution. • The suffix. • The second number.0+ with LinuxThreads 0. a MySQL release must go without any reported fatal bugs for at least one month.37. Otherwise. and is incremented by 1 for each new distribution. expresses the stability of the overall release. if a binary distribution exists for your platform. The MySQL Project recommends that if you are installing MySQL for the first time. All MySQL releases whose names begin with the same number can be counted on to have the same format. However. beta in our example.x with native threads • Linux 2. we can assume that the development branch for this same release is numbered 38.4 Intel and NetBSD 1. because such installs are less complicated than those of a source distribution.3 Alpha • OpenBSD 2.7 • NetBSD 1. or 37 in our example. even if you're implementing MySQL for the first time. then you'll have to work with a source distribution. • The third number. the first choice you have to make before you install the DBMS is that between a development release or a stable release. with no bugs or only platform−specific bugs 204
.1 or glibc 2. you'll most likely choose to install that. without demonstrating any significant problems. Again. if for any reason you need to look at or modify MySQL's C and C++ source code. this number alerts the database administrator to the fact that. To aid you in making this binary versus source decision. you might encounter a release name like
mysql−4. Consequently. As the MySQL Project puts it. ♦ beta: All new code in the release has been tested. represents the release level.21−beta
Here's how to interpret such a release name. ♦ gamma: A MySQL gamma release equates to what most commercial software houses call. Thus. Clearly. that you use the most recent development release.• FreeBSD 3. The Project bases this recommendation primarily on the fact that this release provides crash−simulation and benchmark tests. or 4 in our example. a release. MySQL offers two such levels for every release: a stable branch and a development branch. the Project recommends the latest binary available for your hardware/operating system combination. To graduate from alpha to beta. simply. That is.7. defines a version number within a release level.

Preparing the environment 2. MySQL implements its server as a daemon. It also modifies those tests over time to check for all previously reported bugs.
205
. the shell script that controls installing MySQL Error message files Benchmark test suite Linux daemons
Like so many significant Linux applications that rely on the client/server model. A daemon can also forward such requests to other processes if needed.reported. Installing the compiled suite By default. as outlined in Table 8−4. the daemon that manages jobs scheduled by means of the operating system feature called cron • ftpd.
Table 8−3: Directories Created for MySQL Binaries Directory Bin data include Lib scripts share/mysql Sql−bench Contains mysqld. Further. databases Include (header) files Libraries that MySQL requires mysql_install_db. It's this last state that the MySQL Project calls a stable release. and whose only reason for being is to handle periodic service requests of a particular type. the TCP/IP daemon • initd. the ftp application server • httpd. as well as MySQL client applications Log files. that installation places files in a number of subdirectories in the path /usr/local. Compiling the source 3. Luckily. a Linux system's Web server (most frequently the open source product Apache) • inetd. whether to provide bug fixes or new features. you need not download a new release in order to determine whether it's right for your environment. updates to the suite appear frequently. Important Linux daemons include: • crond. the MySQL server. Tip The MySQL Project does more than run new releases of the DBMS through a set of standard tests and benchmarks. you'll create. A daemon (pronounced like the word demon) is simply a Linux process that runs continuously in the background. The News section of the MySQL Web site describes the contents of each new release in detail. the directories outlined in Table 8−3. the telnet application server
Anatomy of a MySQL source distribution
Working with a source distribution of MySQL means: 1. as a part of that process. which initializes the operating system • telnetd.
Anatomy of a MySQL binary distribution
Should you choose to implement a MySQL binary distribution.

most Linux distributions offer emacs.
206
. of the Free Software Foundation's project to provide a freely distributable replacement for UNIX. you need: • The GNU file uncompression utility gunzip to expand the compressed files that make up the distribution • Preferably the GNU version of the OS command tar • Experience in working with these Linux commands:
cd gunzip ln make
Tip GNU. gcc. a front−end to C compilation. Such files. a text editor much beloved by Linux mavens. whose names are of the format something.0 or higher • A minimum of 16MB RAM • A minimum of 80MB free disk space
Header Files C and C++ header files. yes and no. in addition to the more traditional UNIX universe text editor vi.h. but are not identical. Equally as popular as emacs is the GNU C compiler. the GNU editor that first saw the light of day in the mid−1980s. C or C++ header files info MySQL documentation in Info format lib/mysql C or C++ libraries that MySQL draws upon libexec mysqld. Similar to the online manual or man. as it were. GNU software and Linux interact often. a widely used tool in Linux software development. For instance. that is. a recursive abbreviation that stands for the phrase GNU's Not UNIX. also often called include files. demonstrate the modularity that helps to make these languages so powerful. info nonetheless goes beyond that classic UNIX/Linux help feature by offering capabilities for cross−referencing.Table 8−4: Directories Created for a MySQL Source Installation Directory Contains bin Applications and scripts for MySQL clients include/mysql Include. • A Linux kernel of version 2. • Contain code for such things as input and output • Make that code available to programmers • Are read by a preprocessor. indices. is the nickname. Requirements for installing MySQL To install either type of MySQL distribution. which inserts the code header files contain into the code being compiled at the point at which the header file is named in the latter. the MySQL daemon or server share/mysql Error message files sql−bench Benchmark and crash−simulation test suites var Database and log files Tip Info format refers to the GNU project's preferred online reference. Sound like Linux? Well. which is in texinfo format. a widely available format for Linux online documentation. and easy integration with emacs.

org for a complete listing of these mirrors. rather than from its home base. Table 8−5 elaborates on the example.mysql. A portion of stdio. Installing a binary distribution This example of installing a MySQL binary distribution is straight from the DBMS's documentation.
#ifndef _STDIO_INCLUDED #define _STDIO_INCLUDED #ifndef _SYS_STDSYMS_INCLUDED # include <sys/stdsyms. there are dozens around the world.A classic example of a header file is stdio.h. thereby ensuring that you have the write permissions needed to carry out the installation.h> #ifdef __cplusplus extern "C" { #endif #ifdef _INCLUDE__STDC__ # define _NFILE 60 # define BUFSIZ 1024 # define _DBUFSIZ 8192 /* buffer size for multi−character output to unbuffered files */ # define _SBFSIZ 8 tar
Preparation
The MySQL Project prefers that downloads take place from one of its many mirror sites.
207
.gz | tar xvf − ln −s mysql−VERSION−OS mysql cd mysql scripts/mysql_install_db bin/safe_mysqld &
Table 8−5: Commands Used to Install MySQL Binary Distributions Command or Command Fragment cd /usr/local gunzip < Indicates Change to the path /usr/local.
Installing
This section details installing both binary and source MySQL distributions. the preferred root of the MySQL file subsystem. which involves creating directories and writing files to them
# # # # # # cd /usr/local gunzip < mysql−VERSION−OS. which assumes: • Bourne shell prompts • That you've logged in as or su'ed to the superuser account. which deals with the C library of input and output functions.h> #endif /* _SYS_STDSYMS_INCLUDED */ #include <sys/types.h on one of our machines looks like this.tar. Run the GNU file uncompress utility. Check www.

knows that: It should extract filesIt should operate in verbose mode. in effect an alias.gz
|
tar xvf −
ln −s mysql−VERSION−OS mysql
cd mysql scripts/mysql_install_db bin/safe_mysqld &
Take input for gunzip not from standard input but rather from the file to the right of this symbol. that the file is an archive in a format readable only by the operating system command tar With the suffix .tar. which indicates: In the VERSION parameter. C or C++ programmers thinking of writing code to customize MySQL need to be aware that if they do so. with the command to the left of the pipe automatically handing its output to the command on the right of the pipe. What does this imply about MySQL? Because user−defined functions can't interact with statically linked programs. unarchived binary distribution.
208
. called at runtime.gz. this means that the unzipped MySQL distribution immediately is handed off to the command tar. Run the installation script housed in the subdirectory scripts.004_03 or higher. with the indicated qualifiers x. that the tar file has itself been compressed with the GNU utility gzip That the commands to either side of the symbol. report on every file it processes It takes its input from operating system standard input. interact with no further intervention needed.mysql−VERSION−OS.tar. that helps the executable find its way back to where it started in a series of nested procedures. under the new directory name mysql. but its pointers are defined at compilation. The complete name of the MySQL distribution you're about to install. v. and f. the operating system for which the distribution was compiled With the suffix . Static linking does much the same job. the release name of MySQL In the OS parameter. Test the success of the installation by starting a single−user version of the MySQL server daemon in background. Perl 5. with a dynamic link being a pointer. Statically linked executables: • Are less finicky than dynamically linked code about version questions in the context of OS libraries • Are anywhere from slightly to significantly bigger than dynamically linked code • Can in some cases be slightly faster than dynamically linked code What distinguishes static from dynamic linking? Both refer to pointers. which is called the pipe symbol. means the other side of the pipe with gunzip Use the operating system command ln to create a symbolic link. they'll have to recompile the suite with dynamic linking. In our example. for the unzipped. in this case. that is. especially if MySQL must interact with Perl. Change to the mysql directory ln made available. Which. the input−redirection indicator. Static
MySQL binary distributions use a form of linking compiled modules known as static. which.

though. you must explicitly include the path to this utility in your environment.server start
6. Our example unpacks the distribution under the path /usr/local.In list form. But the way in which you make MySQL aware of the location of this utility differs. and change the path to contain your MySQL implementation's real location. 6. Ensure that the environment variable PATH includes the path to your MySQL installation. 5.45.local):
mysql. Download a distribution file. add that to your environment with commands such as these. which exists on the MySQL mirrors as a compressed tar file with a name of the form mysql−VERSION−OS. 3. The most important subdirectories are: ♦ bin. which houses both the MySQL server daemon and MySQL client software ♦ scripts. # path to mysql executable. and OS holds the operating system flavor that the distribution supports. 7. need to create a password for the mysqladmin account with a command like this:
mysqladmin −u root password []
Tip
substituting the new password for this account for []. 7. you may first. Check the contents of PATH with the command env (for both the Bourne and C shells). and move into it. these commands translate into the following installation steps: 1.tar. Create the MySQL grant tables (necessary only if you haven't installed MySQL before):
# scripts/mysql_install_db
Tip
If you would like MySQL to start automatically when you boot your machine. Should the resulting display not include the MySQL path. just as you did with the overall MySQL path. Change to the MySQL path.
# bin/safe_mysqld &
209
. Depending on your Linux flavor. You must edit the shell script mysqlaccess.server to the location where your system has its startup files. 2. Unpack the distribution and create the root of the MySQL file subsystem:
# gunzip < mysql−VERSION−OS.tar. where VERSION represents a release number such as 3. such as pc−Linux−gnu−i586 for GNU−based Linux OSs running on Pentiums or higher. for the text MYSQL = /usr/local/bin/mysql'. ♦ For the Bourne shell: PATH=$PATH:/usr/local/mysql export PATH ♦ For the C shell: setenv PATH=$PATH:/usr/local/mysql Caution Should you want to use mysqlaccess with a MySQL distribution installed to a nonstandard location.
# cd mysql
In this path.67.gz. In addition. Pick the directory in which you want to unpack the distribution. you can copy support−files/mysql. you'll have to add a line like the following to your startup file (usually the file /etc/rc.d/rc. which contains the installation shell script mysql_install_db that is used to set up permissions for access to the server and its files. at or about line 18. Initialize and test your distribution in safe mode. you see several files and subdirectories. 5. look.gz | tar xvf − # ln −s mysql−VERSION−OS mysql
4.

2. where VERSION is a version number. The former contains an operating system indicator. Change into the top−level directory of the unpacked distribution. configuration involves defining many runtime parameters. Get a MySQL source distribution file from one of the suite's Internet sites.rpm Source code for all the above packages Use a command such as this from the Red Hat prompt to carry out a standard minimal installation./configure −−prefix=/usr/local/mysql # make
Tip Why configure first and only then compile? With MySQL. as with much open source software and Linux itself. an administrator should always confirm the success of a compilation or 'build' before proceeding with other tasks. 1.i386. As a result.rpm MySQL−client−VERSION.i386.Installing a source distribution Installing a MySQL source distribution closely resembles loading the DBMS's binary.
# cd mysql−VERSION
6. Move to the chosen directory with the command cd. with a command like this. you must also load the Perl and msql−mysql−modules RPMs. Unpack the distribution into the directory to which you just changed. MySQL−devel−VERSION. 3. Tip Note the difference between the naming conventions for MySQL binary distributions and its source distributions. with commands such as these:
# .tar. MySQL may also be installed with a Red Hat−specific tool called RPM or the Red Hat Package Manager. the latter does not. These files exist as compressed tar archives.gz | tar xvf −
Such a command creates a directory named mysql−VERSION as it unpacks the distribution file. Tip Currently. with a command such as this:
# gunzip < mysql−VERSION. Decide whether you want to unpack the distribution.rpm
. The MySQL server The standard MySQL client Benchmark and other tests.i386.src. 5. Configure and compile in sequence. Ensure that you have both read and write privileges for the directory you choose. MySQL RPMs are being built under Red Hat 5. and have names such as mysql−VERSION. Consequently.2 but are compatible with other versions of Linux that support RPM and use glibc.
Include the following RPMs in your installation. Installing by means of Red Hat Package Managers As noted earlier in this chapter. which the compilation then includes in the executable.rpm MySQL−bench−VERSION.rpm Libraries and include files needed to compile MySQL client features such as Perl modules MySQL−VERSION. that is. If you load this. and because of the nature of that OS. to install only the MySQL server daemon and clients: 210 MySQL−VERSION. much of MySQL development takes place under Red Hat Linux.tar.gz. 4.i386.

i386. This type of load also creates entries in the system startup file /etc/rc. the suite is not public domain software.org/pub/README. as either a single CD which contains the most current stable release. But on some Intel UNIX systems. and compile source code. with as much more as you can manage.
PostgreSQL
This discussion of installing PostgreSQL assumes that you download.org/pub/CURRENT/
211
. GNU make exists as the command gmake.
Requirements
To create a PostgreSQL executable. or as a subscription entitling you to three CDs • ftp://ftp. Luckily. you must have the following: • Experience in working with the operating system commands gunzip. as another alternative.postgresql. up to 96MB • Free disk space as follows: ♦ 30MB for source during compilation ♦ 5MB for the installation directory ♦ 1MB for an empty template database ♦ 20MB if you want to run regression tests Tip To find out where you stand on free disk space.rpm MySQL−client−VERSION. the University of California holds copyright to it. that tool can be downloaded from the Web site of the GNU Organization at ftp://ftp.pgsql. Tip You can determine which flavor of make your system includes with the command gmake −version.d/ that will start the MySQL server daemon automatically when the installation completes. This syntax reports disk space allocated per file system in KB.i386.postgresql. many Linux OSs offer GNU make as the default compilation−control tool. and after that every time the OS boots. simply try plain old "make". there are few Linux systems on which that standard tool won't do the job. • An operating system from the list of supported platforms at www. Obtaining PostgreSQL PostgreSQL can be obtained from • www.rpm
Tip
The RPM−based installation of MySQL writes primarily to the path /var/lib/mysql.org. Rather. but permits its use under the licensing terms set out in the file ftp://ftp.postgresql. Or. and mv • GNU make Caution PostgreSQL will not compile with any other version of make.# rpm −i MySQL−VERSION.htm • An absolute minimum of 8MB RAM. Should the resulting display not indicate GNU make. Caution As you'll find if you choose to download PostgreSQL from any of the many mirrors on which it resides.gnu. use the command df −k. tar.org/docs/admin/ports. configure.com/pg_goodies/.

conf to determine if this path to online documentation has been properly defined. Table 8−6 offers operating system−specific preparation tasks. In an effort to facilitate downloading. simply type env.gz: PostgreSQL source for interfaces. or /etc/profile for a global profile that affects all user sessions on a system:
PATH=$PATH:/usr/local/pgsql/bin
• Ensure that PostgreSQL man pages and HTML documentation can be accessed with the following environment setting:
MANPATH=$MANPATH:/usr/local/pgsql/man
Since not all Linux systems use the environment variable MANPATH.As of late February 2000. the PostgreSQL group now splits distributions into several smallish files.gz: PostgreSQL documentation • support.tar.gz: remaining PostgreSQL source
Preparation
Get ready to install PostgreSQL by setting a number of environment variables. put the following line in your startup file.5.5MB. or some other.gz: PostgreSQL test suite • base. do so like this: ♦ For the Bourne shell: PATH=$PATH:/usr/local/pgsql/bin export PATH ♦ For the C shell: setenv PATH=$PATH:/usr/local/pgsql/bin ♦ Or. to ensure that PATH can find PostgreSQL from system startup rather than just for the current session.2 /usr/local/etc/ rc. The names of these files follow these conventions: • docs. which can be either .tar. C. be it bash.d/pgsql.conf to set MANPATH. typically /usr/local/pgsql/bin. the downloadable PostgreSQL source distribution took up more than 7.local Task Edit to contain the line su postgres −c "/usr/local/pgsql/bin/postmaster −S −D /usr/local/pgsql/data" Edit to contain the line su postgres −c "/usr/local/pgsql/bin/postmaster −S −D /usr/local/pgsql/data" 1. should you need to modify the contents of PATH.tar.
Tip
Table 8−6: OS−Specific Factors in Preparing to Install PostgreSQL OS NetBSD File rc. You need to download them all. Current versions of 'man' read /etc/man. • Whatever shell you use.1 rc2. libraries • test. Edit to contain the lines:
bin !/bin/sh [ −x /usr/local/pgsql/bin/ postmaster ] && {su −l pgsql −c exec /usr/local/pgsql/bin/postmaster −
SPARC Solaris 2. • Ensure that the PATH on your system includes the location of the PostgreSQL bin directory.tar. To see PATH's current value.sh
212
.d FreeBSD 2. you may have to check the contents of the file /etc/man. Don't be confused by the similarity in these files' names.bash_profile for shell−specific characteristics.

such parameters as the path in which building and installation should take place. Building and compiling the PostgreSQL server need not be done under this account.init. bin./configure
followed by any options you might need. 2. options. if any. with this command. (Most first−time installations require few. Make a symbolic link to this file from the file /etc/rc. Tip Running PostgreSQL as root. 2. and all other users. 2. but can be if you wish.sh
Red Hat Linux
/etc/rc. In any case.d/ S98postgres. primarily for Asian languages ♦ prefix=BASEDIR: Defines a nondefault home directory in which to install PostgreSQL (default is /usr/local/pgsql) ♦ with−odbc: Builds a set of Open Database Connectivity (ODBC) drivers 213
. Create the PostgreSQL superuser account.
chown root /usr/local/etc/rc.).
chmod 755 /usr/local/etc/rc. and in many installations is called simply postgres. type:
. Configure the PostgreSQL source code.init
1./configure −−help
Some of the more commonly used PostgreSQL configuration options are: ♦ enable−multibyte: Allows the use of multibyte character encoding. specifying.d/ postgres. don't do it. This account should have only 'average' file access rights. take these steps. as well as particular features to install or operating characteristics to be taken on by the executable.d/pgsql. For a complete list of options. under which the server runs. or any other OS user account with special access rights is a security risk. but members of the superuser group.d/pgsql. you'll be prompted to log in as this database (as opposed to operating system) superuser. Do all this simply by changing into the src subdirectory of the source code file system.d/rc5. Assign file ownership to the superuser with this command. The postmaster will refuse to start as root. if need be. using the example supplied under contrib/Linux/ in the PostgreSQL source. and typing:
.
Installation
To install PostgreSQL from scratch. Add a file of this name.d/init. Set file permissions so that the root user has all forms of access. when this account needs to come into the installation process. 1.sh
3. or to upgrade from an earlier release of the DBMS. can only read and execute.D/usr/local/pgsql/data −S −o −F > /usr/local/pgsql/errlog' & echo −n pgsql'}
placing line breaks as shown here.

and building and integrating that language interface with PostgreSQL at a later time. you bring down the postmaster (the communications channel between a PostgreSQL server and its clients). As an alternative. Type:
ps ax | grep postmaster
or
ps −e | grep postmaster
to obtain the process ID number or numbers of running postmasters. the PostgreSQL project recommends installing the DBMS without Perl at first. must be installed into a specific point in the overall file system. nonupgraded database server. Type:
gmake install
Caution
Do this step as the user who will own the installed executables. edit the permissions in the file /usr/local/pgsql/data/pg_hba. similar to that shown here. and bring the postmaster back up. but with the generic parameter pid replaced by the actual process ID you learned from ps and grep:
kill pid
or. however. Therefore. in keeping with the sample output above
kill 263
6. If you're upgrading an existing PostgreSQL implementation. 214
. The PostgreSQL group recommends that.conf to allow only you on. The compilation process can take anywhere from 10 to 60 minutes. back up your existing database by using this syntax:
pg_dumpall > db. Ready to install. Again only if you're upgrading an existing PostgreSQL implementation. you need root file access permissions. to carry out this PostgreSQL installation task.out
Caution Make sure that users do not modify or otherwise update data in any PostgreSQL database as you're backing up that database.
263 ? SW 0:00 (postmaster)
Then enter another command. Compile PostgreSQL with the simple command:
gmake
Tip Once again. 3. 5. This need not be the database superuser. Your output from ps should look something like this. as it always does. When it completes successfully. in order to avoid this potentially very destructive combination of circumstances.
4. 'plain old make' is an alternative that few Linux systems will reject. Install the PostgreSQL executable files and libraries. you see this display:
All of PostgreSQL is successfully made.♦ with−perl: Builds a Perl interface PostgreSQL extensions to Perl ♦ with−tcl: Builds interface libraries for and programs that use Tcl/Tk Tip Perl. kill any running. ordinarily /usr/lib/perl.

Enter the series of command shown in this example:
mkdir /usr/local/pgsql/data chown postgres /usr/local/pgsql/data su − postgres /usr/local/pgsql/bin/initdb −D /usr/local/pgsql/data
Caution If you ran gmake (or make) as the OS root user.
/usr/local/pgsql/bin/psql −d template1 −f db.
215
.7. The −D option to the database initialization utility defines where PostgreSQL will store data. 9. don't forget to dump your data back in. tell your system how to find the newly installed PostgreSQL shared libraries. Test your installation. start up the database server in the foreground with a command like this. Any path can be supplied for this parameter.7 or higher Preparing to load Oracle8i involves the tasks described below. working template PostgreSQL data files. Create the database installation.
Requirements and preparation
Oracle8i requires: • At least 400MB free disk space • At least 32MB RAM • Linux 2. log in to PostgreSQL under the database (not operating system) superuser account.0. you need not limit its value to a location under the installation directory. you'll have to be or take on the identity of that user while doing the mkdir and chown just mentioned.
/usr/local/pgsql/bin/postmaster −D /usr/local/pgsql/data
10.out
Oracle8i
This section investigates working with the Oracle8i Installer. But the value defined for −D must be a path to which the database superuser has write permission.34 or higher • GNU C Library version 2. that is. Use a command that follows one of these examples: For the Bourne shell:
LD_LIBRARY_PATH=/usr/local/pgsql/lib export LD_LIBRARY_PATH
For the C shell:
setenv LD_LIBRARY_PATH /usr/local/pgsql/lib
8. If necessary. To do so: First. If you are upgrading from an existing installation.0.

Semaphores track free units of the resource. Those needs occupy two categories: • Kernel parameters • Environment characteristics
Kernel parameters
Oracle8i requires a number of specific values for operating system kernel parameters.LINUX environment setup Before you can install Oracle8i. should equal the maximum number of Oracle processes anticipated Shared memory SHMMAX 4294967295 Specifies the maximum allowable amount of shared memory. thereby ensuring that only one process can use a semaphore at any given time. in bytes.
Environment characteristics
SEMMNI
70
Whether through environment variables or simply by means of commands. you must ensure that Oracle8is environment has the characteristics outlined in Table 8−8.
Table 8−8: Oracle8i Environment Characteristics Feature Significance 216 Value
. you must ensure that the operating system offers the DBMS the environment the latter needs. of a single. you must recompile the OS to make them available. Table 8−7 describes these parameters and the values Oracle8i expects of them. shared memory segment
Number of semaphore set identifiers in the OS SEMMNS 200 Number of semaphores available in the OS Semaphores per set SEMMSL Maximum number of semaphores per semaphore set. track whether or not a resource is available. and make a resource available again after a process has finished using it. Should your kernel not offer these. has no impact on other kernel resources Shared memory and SHMSEG 10 Maximum number of shared memory processes segments that a process can call upon Tip Semaphores are protected variables used to restrict access to shared resources such as disk storage in multiprocessing environments.
Table 8−7: Linux Kernel Parameters Required by Oracle8i Characteristic Identifiers for shared memory Minimum size of shared memory segments Semaphore identifiers Semaphores Parameter SHMMNI SHMMIN Value Required for Oracle8i 100 1 Description Number of shared memory identifiers Minimum size.

source if SRCHOME is set. /usr/bin. and /usr/local/bin Set to 022
. three more for template database Required for databases which use character sets other than US7ASCII Root of the Oracle8i file subsystem Instance name of the Oracle Server. Set to the directory where Oracle8i will be installed Set to a string of four characters or fewer
Set as appropriate to your environment operating system terminal
Defaults to value supplied during installation
Permissions assigned to files Set with the OS command at their creation umask SRCHOME Home directory for Oracle8i Leave undefined until done running the Installer. each Oracle instance running on a given machine must have a unique SID Definition of terminal characteristics for Oracle8i similar to those found in the definitions file /etc/termcap Information about Oracle instances or running copies of the Oracle8i server Search path for Oracle8i
Set to values appropriate to stations from which users will connect to the Oracle8i server
Set to $ORACLE_HOME/lib Must be a member of the group set up for the OSDBA installing and upgrading the
dba and oper respectively
Default: /usr/local/bin At least four
Set to $ORACLE_HOME/ocommon/ nls/admin/data. the Installer searches the location SRCHOME specifies for software to install 217
Must include $ORACLE_HOME/bin. a group must exist for Administrator (OSDBA) role Operator (OSOPER) role Directory that houses shared Oracle8i software Must exist at the same level of the directory structure. the Oracle System Database and for the Oracle System for each of the database thus.DISPLAY
LD_LIBRARY_PATH LINUX user account for installation
LINUX user groups
Local bin directory Mount Points
ORA_NLS33
ORACLE_HOME ORACLE_SID
ORACLE_TERM
oratab file
PATH
Environment variable which defines machine name and monitor type for a user station Location of Oracle8i shared libraries Oracle8i requires an operating system user account dedicated solely to DBMS Oracle8i must have an operating system user group administrative roles it entails. /bin. One for Oracle8i itself.

and their ID numbers and owners. Create a local bin directory in order to provide a common environment for Oracle8i users. which should have these characteristics. You can determine a systems current shared memory and semaphore values. however. because its privileges are simply a subset of the DBA privileges already assigned to the group. Further. Oracle knows these groups as OSDBA and OSOPER respectively. can be any of /bin/sh.Installation temporary Must be set to a directory with at directory least 20MB available space. Set the kernel parameters as outlined in Table 8−7. the DBAs for each installation have access to the other installations. referred to in Oracle8i documentation as the oracle account ♦ Default Group ID (GID) for the OSDBA group ♦ Home Directory: Should share a file subsystem with all other Oracle8i user home directories. there is effectively no OPERATOR role. all mount points defined for Oracle8i must follow a pattern like that shown here:
/oracledb2
This example assumes that Oracle8i software was installed under a path called /oracledb1. Configure the kernel for Oracle8i. or under separate user accounts. ♦ Login Name: Can be anything. Create a LINUX user account whose sole purpose is to own the Oracle8i software that youre installing. Tip You can name the database administrative group anything you like. but defaults to /bin/sh. /bin/csh. The Installer offers the group that you designate as OSDBA as the default choice for the OSOPER group. 3. or /bin/ksh. In other words. But if you call it something other than dba. Members of these groups have DBA or OPERATOR privileges on the Oracle system by virtue of their membership in the corresponding operating system user groups. exist under the ORACLE_HOME directory ♦ Shell: Default shell for working with Oracle8i. need not. the Bourne shell Tip Sites with multiple Oracle servers may install them under the same oracle user account. default: /usr/tmp Tasks to perform as the user root Log in as the operating system root user and carry out the following tasks to set up your environment for the Oracle8i Server: 1. 6. the Installer will relink the executable that its creating. The Installer assigns Oracle DBA and OPERATOR privileges to LINUX groups during Installation. set up LINUX Interprocess Communication (IPC) parameters to accommodate Oracle8i. to which the oracle account has write permission. the groups to which you assign these roles must exist before you begin installing. If you accept the default. with this command:
ipcs
TMPDIR
2. 5. create that group also. Create mount points. If multiple installations share an oracle account. You must run the Installer under this account. In particular. This 218
. Therefore. The Oracle8i Server requires at least four. If you plan to designate a separate group for the OSOPER group. mount point names must: ♦ Share the same root as the Oracle installation directories to which they correspond ♦ Have as their final character a digit that has incremented by one any digit associated with the Oracle pathname 4. Create LINUX user groups for database administrators and operators.

• If your OS doesnt offer this volume management software. Use this syntax:
umask 022
This command ensures that members of the oracle users OS user group. use syntax that follows this pattern:
setenv VARIABLE NAME value
You must set all environment values specified in Table 8−8.login
Installing
Take these steps to install Oracle8i. 3. Set environment variables in the . /usr/local/bin takes this role for Oracle8i implementations.directory should be outside the ORACLE_HOME path. 2.profile or . but not write permission. Typically. Update the environment. After setting environment variables. and all other users on the system. or use the command su to take on the identity of. While the oracle user account owns this file. Wherever you place an Oracle user common environment. to all files the Installer creates. the file lives in a directory that requires root user privilege if it is to be manipulated. Tasks to perform as the user oracle Log in to the oracle account and perform these tasks: 1.sh provided on the Oracle8i distribution CD−ROM to create the oratab file and set its permissions. will be mounted automatically to the mount point /cdrom/oracle as soon as you place it in its drive. in RockRidge format. For the C shell:
$ source . the operating 219
. you must mount the CD−ROM manually.profile
4. following one of these patterns: For the Bourne or Korn shell:
$ . Create the oratab file./. Run the shell script orainst/oratab. Therefore. use syntax that follows this pattern:
VARIABLE NAME=value export VARIABLE NAME
Tip
For the C shell. For the Bourne shell. make sure that every Oracle user has this directory in his or her PATH and has execute permission on the directory. But note first that: • The volume management software originated with Sun Microsystems Solaris. Use the umask command to check current settings for file−creation masks. you must be logged in as. Oracles Product Installation CD. 7. update the environment in the current shell session. thereby allowing you to begin the Oracle8i Installer immediately. 7. have read and execute. Set the permissions to be assigned automatically to newly created files.login file of the oracle user account before firing up the Installer. but is now available in many Linux flavors.

Allows you to specify why you want to use the Installer. then drop the shell you started as the superuser. Upgrade.system superuser. or De−Install Software. These prompts appear regardless of the task you are performing or the products that you are installing. which moves you forward through screens. Use commands similar to these. and begin with that task. which selects fields. 4. that tool prompts you to confirm the values of ORACLE_BASE and ORACLE_HOME. Create/Upgrade Database Objects. Use the command su to temporarily become the oracle user./orainst
Tip Basic navigation techniques needed to work in character mode with the Oracle8i Installer include the Tab key. with a command such as this:
cd directory_for_CD_mount
5.
Installation location
If youve set the environment variable ORACLE_BASE before starting the Installer. substituting a path name for the CD mount point thats appropriate to your environment. as well as for the ORACLE_HOME directory. If ORACLE_BASE is not set. This section describes these initial Oracle8i Installer prompts. but supply parameters appropriate to your environment. If you choose default. includes: Install. The steps we list here assume that you must mount the Oracle8i CD manually. 1. the Installer prompts you for a software mount point. which can be done with or without creating database objects • Add/Upgrade Software An Oracle8i server can be loaded with either of these options. 220
. If one does not already exist. Become the root user. Perform Administrative Tasks
Installation Activity Choice
Installation options
The Installer offers two types of installation activities: • Install New Product. which move you between fields. Mount the CD−ROM drive to the appropriate mount point directory. Installation Type/README Files The Installer offers a choice between a custom or default installation. Change directories to the mount point that you just created. Again. create a directory that will act as a mount point for the CD−ROM. use commands similar to those here.
$ su root # mkdir directory_for_CD_mount
2.
# mount /dev/OS_designation_of_cd_drive directory_for_CD_mount # exit
3. and the spacebar. the Installer displays the settings it will use and asks you to confirm them. Initial installer prompts An Oracle8i Installer session consists of a series of prompts. each displayed in its own window. Launch the Installer in character mode with this command:
. arrow keys.

sh script
The Installer creates a shell script called root. Caution Among the items listed in the Available Products window is the Oracle8i Installer itself. the Installer will prompt you to learn whether it should append new commands to the existing script or to create a new script. Also.
Software asset manager
In the prompt labeled Software Asset Manager.
Install source
At this Installer prompt. for instance. Be sure to select this product if you anticipate installing documentation that applies to all Oracle8i products 221
. they are saved under names in the pattern of somelog. another area of a system or a network file structure. The operating system superuser must run this script immediately upon installations completing.old.Installation log files
To record its work. Tip Should root. Be sure to enter the correct response to this latter prompt. Tip Installation logs from an immediately previous invocation of the Installer are not overwritten. Tip Any definition of display language that you make with the National Language Support prompt can be overridden. you must specify whether you are installing from CD−ROM or from a staging area.
National language support
At this prompt. Tip In addition to letting you pick products. Users or client applications can also set this parameter. that is. These files track: • Actions taken that affect the operating system • Actions that rely on the Installer makefile • Actions that use SQL statements • General Installer actions By default these logs reside under $ORACLE_HOME/orainst. If you specify a staging area.sh in $ORACLE_HOME/orainst.S. this window provides detail on some product categories. instead. the Oracle8i Installer creates four log files. Oracle Corporation recommends doing the latter in most cases and suggests appending to an existing script only on those occasions when specific Oracle8i characteristics must be preserved.sh already exist. that is. then just click Install. you can specify a language other than U. where those products will be placed. this time to say whether the staging area is temporary or permanent. or select it and press Enter in character mode. select the Oracle8i products to install from the Available Products window. the Software Asset Manager tracks space available in the directory. English in which screen messages from Oracle8i should be displayed.
Location of the root. then you need only double−click the category name in graphical mode. if you want to know what specific products fall under the banner Protocol Adapters. youll be prompted again. So. in ORACLE_HOME. because the Oracle8i Installer deletes temporary staging areas as it finishes with them during installation.

you choose the operating system user group that will receive Oracle DBA privileges. Oracle Corporation strongly recommends that you spread your database across at least three devices.
Mount point locators
Oracle Corporation recommends that the database mount points you define to this prompt differ from software mount points you provided to the initial Installer prompts. Tip Under Linux. While the Installer wont object if you define only a single mount point. youll see another series of prompts. both the template database that youre creating and the log files spread out over the mount points you specify. you define the character set in which the database will function and store data. Frequently.regardless of their OS platform. This setting defaults to the group to which the oracle user belongs. the default is US7ASCII. you must say whether you want the Installer to adhere to the recommendation from Oracle Corporation to spread database objects across at least three mount points. Caution If you specify a database character set other than the default.
Storage type
In this window. or allow them to default to the group you specified as OSDBA. you can specify whether databases will be stored on raw devices or within a file system. a string whose value is the same as that of the DB_NAME initialization parameter Database creation prompts If you use the Oracle8i Installer to create a database.
Instance name
Use this prompt to set the Oracle8i SID to: • A string no more than four characters long • In single−instance installations. a raw device is one that has not been formatted to hold files.
OSDBA group
In this window. raw devices house such resources as swap space. Oracle8i somewhat breaks this OS convention by allowing you to place databases on a raw device. you must also have set the environment variable ORA_NLS33 during preinstallation. as discussed in this section.
Number of mount points
At this prompt. If you havent. you can give Oracle8i OPERATOR privileges to a distinct Linux user group. an error may 222
. As you might imagine. If you take this option. or if you simply want to have the Installer more easily accessible on your hard drive.
OSOPER group
Here.
Character set
Here. or mount points on a single drive.

however. To install operating system−specific documentation. Verify that the Installer exists on your file system. 7. or both formats for the documentation youre loading. 4. must be installed during its own. a storage character set cannot be changed without recreating the database. arrives with the Oracle8i distribution set either: • For OS−specific documentation. Tip An Oracle8i distribution CD offers both operating system−specific and product documentation in HTML and PDF formats. Click Install.
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. or De−Install Software.
SYS and SYSTEM user passwords
Oracle Corporation strongly recommends that you use this prompt to change both these built−in Oracle8i accounts passwords. Product documentation. If it does not exist on your file system. Start the Installer from the hard drive rather than from the CD. Otherwise. though. on a separate CD−ROM Both categories ordinarily are loaded during an Installer session. load it. a user must: • Be a member of the operating system group or groups to which you assigned DBA or OPERATOR roles • Enter the passwords you supply to this Installer prompt Installing documentation Oracle8i documentation. simply choose LINUX Documentation from the Available Products window during an overall Installer session. select Oracle8i Product Documentation. At the Installation Activity prompt. 6. choose Install Documentation Only. Upgrade. At the Installation Options prompt. 2. Oracle8i allows clients to use a character set other than the storage set. choose Install. A loophole does exist.
The dba and operator group passwords
To connect to an Oracle8i database as either a system/database administrator (SYSDBA) or system/database operator (SYSOPER).
National character set
In this prompt. you must take these steps: 1. on the Oracle8i CD−ROM • For product documentation. Further. be aware that once its defined through the Installer. this parameter defaults to the database storage character set. you can define a second character set for use with specially declared fields. however.occur. PDF. separate Installer session. Indicate HTML. From the Software Asset Manager. or. 5. To install product documentation. in character mode. select Install and press Enter. product−related forms. 3. in both operating system−specific and in generic.

pay particular attention to these factors: • Disk and memory requirements • Whether to install a pre−compiled executable or to obtain and configure.Summary
When installing a Linux DBMS. specific to your environment • Kernel characteristics needed by your chosen DBMS • Environmental characteristics your selected DBMS must have • Installation and configuration tasks which must be carried out as the user root
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. by compiling.

or data dictionary. I review the most significant of these techniques here. in turn. that model is often converted into tables that define the logical relationships between areas of data that the database must reflect. Such modeling attempts to understand the inherent nature of the data to be processed. This section discusses techniques that can contribute to effective schema. Logical modeling Upon completion of an object model.
Data modeling
Modeling data as the first or one of the first steps in database design seeks to ensure accurate abstractions of data. to help preclude • Erroneous data • Field data types that are not consistent across tables • Fields that may not be available to all applications • Missing data • Redundant data Table 9−1 summarizes data modeling as presented. Physical modeling Physical modeling is the keystone of schema design. These facts. data modeling uses techniques such as end−user and operator interviews in an attempt to identify and completely correctly define required data.
Effective Schema Design
A database that relies on an inefficient schema is of as little use as a building whose blueprints fail to depict all rooms or entrances. while at the same time precluding duplicate data items. You can choose from a number of data modeling techniques. Object modeling An object model is a collection of facts or groups of facts (that is. serve as the basis for identifying individual data items.
225
. So. This process of modeling the database logic takes place in spite of the fact that the model may not yet contain all the data items that the DBMS will ultimately house. because it involves creating the initial schema based on the relationships and entities defined during object and logical modeling. words and phrases) that describe the environment in which the database must function.Chapter 9: Configuration
Preparing to set up a database under Linux starts where such preparation would under any OSwith the analysis and structuring of the data the DBMS must manipulate. it is even more critical than at earlier design stages to analyze data definitions as they are being supplied. During physical modeling. design. apart from any situational or operational qualifiers that might affect the data.

smoother learning curve. understanding and employing normalization techniques can benefit the schema that results from the data−modeling process. On the other hand. for example. helps ensure a complete and correct schema Implementing the database Use the physical model as structure. Table 9−2 summarizes what I consider the most important normal forms to keep in mind when modeling your data. which will influence the manner in which the database can manipulate data. a number of records in Table B might match any given record from Table A No Normal Form (that is. for example. that is. by incorporating not only data and relationship definitions but also constraints such as the manner in which operator skill levels or equipment might affect the accuracy of data input. Helps Ensure that all entities with which the DBMS must deal will be identified
Normalization
Its not necessary to be scrupulous in applying relationship theory to data modeling.
Table 9−2: Normalization This Normal Form Second Normal Form (two functional dependencies. no functional dependencies) A database without relationships
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. the a template schema Accurate modeling not only helps to ensure an accurate database.Table 9−1: Data Modeling Stage of Modeling Defining the overall database structure Task Create an object model Create a logical model Use the logical model as the basis for creating a physical model that all relationships between entities. such a step−by−step approach helps to ensure input from and feedback to end−users. in which. will be identified physical model. a single field from a record in either of two tables will reflect the relationship) Involves This Type of Relationship A one−to−one relationship. that is. in which. but it also helps provide for • Less correction and redesign down the road • The independence of the database from hardware or operating system platforms • The capability of the database to work seamlessly with applications other than the DBMS that must manipulate it Further. therefore. Table A and Table B have the same data item serving as the key. and from which. in turn thereby assuring them a shorter. only one record in Table B will match any given record from Table A First Normal form (one functional dependency) A one−to−many or many−to−one relationship.

the nature of the data manipulation language that your Linux DBMS makes available can influence how you structure your data in the first place. the DDL enables you to identify to the database application: • Tables • Fields within tables • The nature of the data to be contained within those fields (that is. all Linux databases possess a critical feature: the data definition language DDL.Joins
Another way of looking at relationships between tables is to examine them as joins. Based on those relationships and the sample data shown in Figure 9−2. a new table will result when a join is carried out on these two. In general. A join can be defined like this: If you have two tables. as shown in Figure 9−3. respectively. which reflects. one called Table Y and the other Table Z. consider the table designs depicted in Figure 9−1. a one−to−one and a one−to−many relationship. new tables would result from each of these joins being carried out.
Figure 9−2: Sample data for joins Figure 9−3: The result of joins
Data definition language
While syntax differs from DBMS to DBMS. Any data manipulation language (DML) should provide the capability to: • Insert data • Delete data • Update or modify data • Retrieve or display data
227
. which have a field in common. However. field length and data type) • The field that will serve as the key for each table • Any additional indexing to be applied to tables • Relationships between tables
Data manipulation languages and schema design
It may seem to be putting the cart before the horse to discuss data manipulation in a section on schema design. The appropriate DDL must be used in building a schema. For example.
Figure 9−1: An example of a join This design presents the possibility for both an inner join and an outer join.

might begin to construct a query in this way.
Table 9−3: Data Manipulation Languages Effects on Schemas And Therefore Need have little effect on schema design Remove Uncomplicated Need have little effect on schema design Update/Modify Uncomplicated Need have little effect on schema design Retrieve/Query Unclear.. a well−designed schema can help do the same. conditions. affects schemas by focusing designers attention on the structure of individual tables. This DML Function Insert Often Perceived by Users As Uncomplicated
Database query languages and schema design
Literature on relational databases frequently discusses three major types of database query language: • Procedure−oriented • Tuple− or record−oriented • Domain− or table−oriented A procedural query language.plant_name. a domain−oriented query language uses its variables and expressions to bridge domains rather than to bridge relationships. v. such as IBMs SQL. because users may not Requires schemas to be set up to know what to look for. or query languages. and WHERE to create joins.plant_description. QUEL. FROM. the query language of INGRES. and formulas. have been designed to take up this slack.
range of p is PLANT_DESCRIPTION range of v is VARIETIES retrieve (p. A tuple− or table−oriented query language uses variables.variety. uses keywords such as SELECT. or they may cause the relationships between state their requests for data data items to be immediately subjectively or in a disorganized apparent to the user way Because of the difficulty many users have in clearly formulating requests for data.parent_plant_name)
Finally. However. p. • The record−oriented type of query language. being perhaps the most straightforward type of query language. data manipulation languages.Table 9−3 summarizes the most significant ways in which the nature of a DML can impact your schema design. One can see that the differences in how these categories of query languages operate might present constraints to schema design similar to these: • The procedural type of query language. v. by highlighting the relationships between data items. one such language. being as much table− as relationship−oriented. focuses easily on relationships and thereby aids in cross−table schema building.
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.

the performance required of your database. How big might such files become? How often does the DBMS allow you to trim them? • Consider the demand for storage such user−related features of the DBMS as individual and group profiles will make. manipulation.
229
.
Storage
In addition to defining your databases schema for complete and accurate storage. and retrieval of data. striping as weve just described it or other RAID techniques need introduce no complications to managing a database. and how I/O hardware must be configured to serve your database efficiently. you must also: • Consider the demand for storage such administrative aspects of the DBMS as log files will make.Capacity Planning
You cannot effectively plan a database or create its schema without considering the demand for system resources that the database will make. The DBMSs initial settings should suffice. and whose volume of data stored is expected to grow only at the rate of about ten percent annually. which is notorious for its lackadaisical nature.
RAID
Using a form of RAID (redundant array of inexpensive disks). to spread data across a number of physical drives can improve database throughput. in order to have a sound basis for extrapolating the amount of disk storage data files will take up as actual data is entered into them. This section discusses three categories of such demands: storage. physically. data may be spread across several drives. For instance. theres little need to fine−tune either DBMS or the I/O or data communications upon which it relies. Ask yourself questions such as: • How many tables do I really need to accurately represent my data and the relationships among the data? • How closely and to what degree of detail must I monitor activity in the database? • At about what rate do I anticipate the volume of data stored will grow? The answers to these questions will influence maintenance of your database. only one logical drive exists. if you anticipate seven tables in a database that must be monitored only once a month. and processing. memory. • Carefully note the record size of each table as you define your schema. From the point of view of the database administrator. by relying on parallel data access across multiple files. even though. Figure 9−4 depicts an example of RAID as it can be implemented in Linux DBMSs. thus.

Tip Whatever form of RAID or mirroring you settle on. A third storage option that is available for most Linux DBMSs combines striping all data with the striping and mirroring data that is the most difficult to recover or reconstruct (for example. remember that you will need twice the number of drives you otherwise would have employed. with throughput significantly reduced. remember that the larger the array and volume of data handled. or a total of eight. the decision to use random or sequential access in defining striping can also affect performance improvements. that is. to mirror a database that had been implemented on a four−drive array. the more time the DBMS and OS require to update parity and other RAID management information
Defining Inodes An inode can be defined as a data structure holding information about files in a UNIX or Linux file system. having a high number of drives may impede database performance. Also remember that the more your database is weighted toward write operations. Every file on such systems has its own inode. schemas and logs). Another technique recommended by several Linux DBMS vendors seeks to further ensure data reliability and DBMS up−time by combining RAID levels 0 and 1. and so on. as well as the number of disks involved. Tip Stripings effectiveness has a very direct relationship to the particular flavor and release of Linux that underlies it. then writing the second block to the second such disk. Finally. The folks at MySQL as well as other Linux database gurus recommend benchmarking your DBMS with different stripe sizes in order to determine which size provides optimal database performance. which helps not only to identify the file within the operating system but also within the particular file system in which the file lives. Every inode identifies:
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. cost can quickly become a determining factor. For example. Of course. that is. if the size of a typical write operation is less than or precisely equal to the defined stripe size. in such an implementation. your database will perform much better. Under such a scheme. can give performance differences several orders of magnitude apart from one another. by using both striping and mirroring in implementing your database. The larger the number of writes. Note also that the exact way in which striping parameters are defined. you would need an additional four drives. the more likely you will be to require additional software tools to manage that volume efficiently.Figure 9−4: Striping and mirroring under MySQL As MySQL interprets it. striping involves placing the first block of data to be stored in your database on the first disk in your RAID array. Should you take this path. toward addition and modification rather than toward retrieval.

231
. way of optimizing disk usage by your database is to mount the file system within which the database resides with the noatime option. large GNU C Compiler (gcc) compilations. does. that is. For those of you who are curious about very small details. while not exorbitant.5 to 2 times the amount of RAM. an inode does everything and more than one of its analogs. a record in a File Allocation Table. whose default size is 64K • A connection buffer • A result buffer Both the connection buffer and result buffer are dynamically allocated. as a rule. a files inode number can be found using the −i option to the command ls. and can grow to provide for the maximum number of packets permitted.
Perhaps the simplest. be reduced to 1. heavily stress memory. are not trivial either. in order to help preclude unnecessary demands on memory. If you have not compiled shared memory support into your kernel. in designing your schema. Swap space requires three times the amount of physical RAM. thereby avoiding at least a few some disk seeks. Therefore. Also remember that some Linux DBMSs may have to be compiled and that such tasks. you need to recompile Linux to add this feature in order to avoid core dumps that might otherwise result when certain DBMS administrative utilities are run. Tip In systems with more than 1GB RAM. A minimum of 48MB is required for RAM. and resulting in better disk and DBMS performance.
Examples of demands on memory: MySQL
Every connection to a MySQL database server uses several thread−specific memory spaces: • A stack. Tip Another aspect of memory management that can plague a Linux DBMS involves shared memory. but certainly in the case of relatively small databases the most efficient. make every effort to keep it as tight as it is correct.• The physical device in which the inode resides • Locking information for the file the inode documents • Access mode for the file the inode documents • Type of file the inode documents • Number of links to the file the inode documents • The user and group IDs of the file the inode documents • The number of bytes in the file the inode documents • Access and modification times for the file the inode documents • The time the inode itself was last modified • Addresses of the files blocks on disk That is. the amount of swap space required can. This option directs the operating system to forego updating an inodes last access time.
Memory
Memory requirements for Linux DBMSs.

enabling parallel query execution could benefit overall performance. with n representing maximum row length.
Processors
To design your database for optimum performance and to configure it and its OS platform for the same. Given these and other similar characteristics of MySQL. When each backup device can be written to or read from concurrently. a number that will allow it to dovetail its handling of user requests without short−changing any individual user on processing power. conciseness in schema design becomes even more imperative than usual. Note Examples of operations that can benefit from parallel execution include joins of large tables.
Redundancy and backup
In database parlance. Ordinarily. but also on processors. or to the immediate availability of one or more duplicate copies of the database which can be brought online immediately in order to minimize downtime. use either thread−scheduling utilities provided by the DBMS. with most joins handled without the need for temporary tables. especially in environments with very large databases. redundancy can refer either to the capability of a database server to run as many operations as possible in parallel. and the relevant index and data files opened only once for each concurrently−running thread. to optimize use of the processor and achieve greater throughput. Further. such a cache contains 64 entries.
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. and a buffer of size (3∞n) is allocated. For CPU−intensive databases and their applications. and the sorting of large result sets. configure your database server with an optimum number of concurrent users. that is. column structures for each column. with memory allocated only for unexpectedly large strings. Any tables that might be required are by default memory−based. none of MySQLs operations involve memory mapping. multiple backup devices can decrease the time required for backup and restore operations. For each such thread. all joins are done in one pass. Queries that must examine large numbers of rows. Almost all of MySQLs parsing and calculating is done in local memory. consider using either multiple backup devices or permitting your database server to use parallel I/O to increase the speed of backup and restore operations. especially for servers whose hardware platforms offer less than generous memory. Backup. you must keep in mind. As much as possible.MySQL supports up to 4GB RAM. substantial aggregations. If your DBMS supports multiple CPUs. a table structure. not only demands on memory. Table handlers for all active tables reside in cache and execute as First In. simply refers to the capability to provide the latter form of redundancy. every request doing a sequential scan over a table allocates a read buffer. If possible under your Linux implementation. heap tables. Rather. which are therefore CPU−intensive. of course. or operating system tools such as nice. that is. First Out (FIFO) operations. managing it through a 32−bit memory space. can benefit from being run in parallel. As a result.

Table 9−4: Linux and Wildcards Linux Interprets a* a? As Meaning the Pattern any string. whose first character is a lowercase a. they replace.log and Database. respectively: • A question mark (?) replaces a single occurrence of any character. That syntax is:
. can expedite your configuring a database under it by reviewing the concepts and commands discussed here. a5./script_name
For example. aa.
/directory/where/the/script/lives/db_cleanup
Tip To preclude voluminous typing such as that in the previous example. ab. you would type something similar to this. however. So. to run a script called db_cleanup from the directory where the script lives. and aA would all match this notation. whose first character is a lowercase a. as in the Microsoft. proceed to the next section. that is. ab. Those of you new to the OS.Initial Configuration
Successfully configuring an RDBMS under Linux requires a solid grasp of certain basic concepts and commands. Table 9−4 provides some examples of using wildcards under Linux. I begin this section by reviewing those Linux features. ak. the characters ? and * act as wildcards. aa. if you like. of no more than two characters. 233
. The patterns a. include the path or paths where database maintenance scripts are likely to be housed in your PATH environment variable. any string. the great majority of your typed conversations with Linux commands will be rendered in lowercase. • An asterisk (*) replaces any number of occurrences of any character or characters. and aA would all match this notation. Executable scripts Under the Bourne shell.log. a special syntax must be used to run user−written command files or shell scripts. of any number of characters. you must distinguish between the filenames database. for instance. Linux will do so. Wildcard characters In the Linux universe. be assured. the default command−line interface for most flavors of Linux.
Linux concepts and commands
Those of you with a long familiarity with Linux can. a1drgnkj73. Case sensitivity Linux is case sensitive. abc. you could type:
./db_cleanup
To run that same script from a directory other than its native one. The patterns a.

Symbols Linux gives special significance to the characters discussed in this section./does_a_lot &
In response. and then return control of your station to you. as it does all tasks. The patterns c32[59umynljd. cyd.
Figure 9−5: Linux lets you know that its accepted a job into background. bb. which defines the areas of the file system in which Linux will look for data or commands. if you wanted to run a shell script called does_a_lot. whose last character is a lowercase b. and ends in a lowercase d. but with the value stored under that name. ab. 4b. by means of a Process Identification Number (PID). any string which begins with a lowercase c. and Bb would all match this notation. not with the variable name itself.
Ampersand
The ampersand (&) tells Linux to place a job in background processing. and file names. the dollar sign ($) has two meanings to Linux: • It can be used as a command−line prompt for ordinary users.
234
. contains any number of other characters after that. contains the value /usr. • It can be used with environment variables. the forward−slash character (/) indicates the root directory to Linux. and carries out specific actions when it encounters those characters. to tell the shell to deal. The patterns c2d. if the environment variable PATH.*b ?b c*d
c?d
any string. that is. and tracking it. of any number of characters. dcb. of no more than two characters. cap84od. or at the beginning of a pathname. and cd would all match this notation. and cd would all match this notation. you could use this command. users other than the superuser root. subdirectory.
Dollar sign
Like the forward slash. For example. bb. any string. Linux would issue a message like that shown in Figure 9−5. The patterns ab. any string which begins with a lowercase c. freeing your station for other.
. The patterns b. foreground work while still plugging away on the background job. and ends in a lowercase d.
Slash
By itself. which ordinarily takes about four minutes to complete. then the value of $PATH is /usr. c0d. and +b would all match this notation. but didnt want to tie up your machine for that length of time. slashes separate directory. For instance. whose last character is a lowercase b. Within a path. contains any single occurrence of another character after that. a1drgnkj73b.

db > list_of_databases
Caution Note that. to store the output of the ls command in a file called list_of_databases. But.
Input redirection
Should you need to take a commands input from somewhere other than its default source. which produces a long listing of files in the current directory. and redirect the files contents to echo.
Output redirection by appending
To store the output of the ls command in a file called list_of_databases. if the indicated output file already exists. you could place that text in a file. such a command completely overwrites it. the less−than symbol (<) tells Linux to do so. known in Linux as standard output).db >> list_of_databases
The double greater−than symbol (>>) causes Linux to append to.
Output redirection
If you need to send a Linux commands output somewhere other than to its default destination (almost always the monitor. in the current directory. and at the same time avoid replacing earlier contents of that file. Figure 9−7 illustrates this technique. the echo command ordinarily expects its input from the keyboard. rather than replace. existing file contents. weve piped the output of the ls −l command. use this syntax:
ls *. For example.
235
. which searches for the pattern trek in any of the files in that listing. In the example below. For instance.Pipe
Should you need to combine Linux commands in such a way as to automatically pass the output of one command to another. and produces output like that in Figure 9−6. you could use this syntax:
ls *.
ls l | grep vulcan*
Figure 9−6: Piping from ls to grep to find files whose names contain the string vulcan. in the current directory. which will use that data as input. to the command grep. if you want to display standardized text. you need to use a pipe ( | ). you can do so with a single greater−than symbol (>).

jason::18:2::/home/mysql/jason:/sbin/sh
Colons separate fields in the values associated with the environment variable PATH. Colons separate fields in the Linux password file /etc/password. it is usually restricted to system administrators. allow you to carry out tasks denied to most users.
clear. ls l | grep *db Colon
In the context of system and database administration. making it of more immediate importance to the OS and 236
.
Semicolon
If need be. cd /. that is. however temporarily.
Altering processing priorities
Assume that youre in the midst of compiling. no password. or simply to speed up typing and execution. those areas include the directories associated with the DBMS. that is. Because the root login conveys such extensive powers. privileges usually available only to a Linux system administrator. configuring by means of a gcc compilation. and the home directory /home/httpd/logs. You can speed up this or any other command by raising its processing priority. in the following line. changing file and directory access and execution permissions. colons enable us to distinguish that the user in question has the login name jason. Assume further that this task is taking far longer than you had anticipated. In the following PATH. Contact your system administrator for the required login name and password should you need to function. Linux commands can be strung together one after another. as described in this section. by separating them with a semicolon (.) like this. the colon (:) has two significant roles. a Linux DBMS. which in turn defines those areas of the file system that Linux will automatically examine for data or programs requested by a user.
Logging in as the superuser or root
Root user privileges. among other things. For example. you must carry out a number of common operating system administrative tasks. and creating user accounts.
PATH=/usr/sbin:/usr/bin:/home/oracle8
Basic Linux tasks To configure any DBMS under Linux.Figure 9−7: Frequently used messages can be supplied to commands with input redirection. as root. These tasks include altering processing priorities.

chmod 6xx or x6x or xx6 filename Add read and write permissions to the indicated user. The octal digit 6 translates to binary as 110. but not write. which three digits can be read as enable read and write. The capability to modify the contents of a file or directory will always be indicated by the letter w in such a listing. or execute permission to a file for members of that files owners user group. thereby raising that commands processing priority.
Changing file and directory access permissions
Linux organizes file access permissions into three groups of three permissions. because the octal digit 4 translates to binary as 100. write. 237 This Syntax chmod (+/ r or w or x )u filename
. youd only need to do one more thingissue the command nice with the following syntax. chmod 7xx or x7x or xx7 filename Add all possible permissions to the indicated user. the center three columns to users who are members of the owners user group. but not execute. and the last three columns to all other users of a system. The first three columns of the output of ls −l apply to the owner of a file or directory. Similarly. Table 9−5 summarizes how these permissions relate to one another and to the overall status of a file. also often called world. chmod +wxg myfile would add write permission but remove execute permission to the file myfile for members of the owners user group.
nice −− 10 gcc my_database
This command would lower by 10 the nice number associated with the indicated command. The octal digit 5 translates to binary as 101. Also enable execute permission. or or execute permission to a file for the user population chmod (+/− r or w or x )o filename at large. write. members of the owners user group. with lower numbers denoting higher priorities. while permission to read a file. but deny those same permissions to members of the owner user group. permissions.
Table 9−5: Changing Linux File Permissions Allows You to Add (+) or remove () any or all of read.CPU. and execute permissions. It offers read. chmod 700 would grant all available types of permissions to a files owner. which three digits can be read as enable read. Linux sees the hierarchy of execution as having an inverse relationship to nice numbers. To do this. The letter x in a long listing of files indicates the capability to execute. youd need to be logged in as root. write. For example. for the world or others. The octal digit 7 translates to binary as 111. which includes being able to see its name in listings. write. Tip Pluses (+) and minuses () may be combined in a single command. chmod (+/ r or w or x )w filename Add (+) or remove () any or all of read. chmod 5xx or x5x or xx5 filename Add read and execute permissions to the indicated user. write. permission. which three digits can be read as enable read. as well as to the user population at large. chmod 4xx or x4x or xx4 filename Enable only read permission for the indicated user. that is. chmod (+/ r or w or x )g filename Add (+) or remove () any or all of read. and execute permission for files and directories to the owner of the file or directory. or execute permission to a file for the user who is that files owner. is denoted by an r in the output of ls. If thats the case. and everyone else on the system.

and must be replaced by actual environment variable names or values.profile • For the C shell. a somewhat different syntax is needed.
$ groupadd −g 101 dba
Oracle documentation refers to the database administrator and operator groups as OSDBA and OSOPER respectively. or database administrator.profile or .Creating user and group accounts
You can use the Linux utility groupadd to restrict access to database administration functions to designated users. Linux environment variables specify.login file. as the groups that were granted Oracle DBA. For example. the terms variable_name and value here are generic ones.
Setting default file access permissions
The Linux command umask sets default access permissions on all newly created files on a system. To apply such permissions to any new files created under the login name db_user.profile or . or database operator.login file of the login account or accounts which connect to the database server. and then makes the shell aware of that value by means of the command export. the command line below sets the home directory for Oracle to /usr/app/oracle/product/805 by means of the syntax variable=. For instance. Environment variables for a Linux DBMS are usually set in the . but not write permission. . youll have to reboot your Linux database server to make such changes take effect.login
Setting environment variables
Every Linux shell has what are called environment variables. and its contents applied to your database session.
ORACLE_HOME=/usr/app/oracle/product/805. (Of course.login file of that user account: • For the Bourne or Korn shells.) For example. For the Bourne or Korn shell. enter the following in the . The appropriate file is read automatically when you connect to that server. In carrying out database administration. type:
$ . and Oracle OPER. your file permission settings. the line below accomplishes. in the OS group file /etc/group. you can ensure that those new values will be in force immediately by executing the . Such variables hold values that define the characteristics of a user session. add umask 022 to . Oracle8i recognizes the Linux user groups dba and oper. add the same line to the file . privileges. youre likely to use the value 022 most frequently. the printer you use. among other things. to give read and directory search. to specific users. and the colors displayed on your monitor. with only the setenv command. use the following syntax: variable_name=value. For example. export variable_name. what the Bourne shell needed two commands to do.profile or . Should you not do so.
setenv ORACLE_HOME /usr/app/oracle/product/805
Tip When you change the values of environment variables. This syntax does not require the command export. export ORACLE_HOME
To set an environment variable in the C shell. Use a command similar to the one below to create these groups if theyre not already present on your system. To set an environment variable in the Bourne shell.profile
238
.

While not all Linux DBMSs require it, the administration of your file system can benefit if you create a mount point directory that will act as the highest level of your DBMS directory structure. Should you take this step, make sure that: • The name of the mount point you create is identical to that which was originally assigned to your DBMS software • The DBMS administrator user account has read, write, and execute privileges on any database mount point directories you create

Generic configuration tasks
With such Open Source products as MySQL and PostgreSQL, configuration is almost completely synonymous with installation. That is, configuration of such DBMSs involves: • Obtaining the appropriate distribution • Unpacking the distribution into the appropriate directory • Changing your working directory to the uppermost level of the distribution subsystem • Compiling and simultaneously configuring, by means of options supplied to the compilation • Initializing and testing the configured DBMS

Vendor−specific configuration
This section discusses vendor−specific configuration tasks relating to three widely used Linux DBMSs: MySQL, PostgreSQL, and Oracle8i for Linux. MySQL To begin to configure MySQL, you must first select a directory to house it and then unpack the distribution file.

Configuration Options Examples of common configuration options include: • Compiling only client libraries and executables while foregoing server compilation • Compiling to place log, and even database, files in a specific directory • Compiling to produce a statically linked executable (sometimes recommended for speed) • Compiling to suppress or require use of default, or non−null, values • Compiling to require a specific character set for data and sorting • Compiling to provide debugging • Compiling to provide for or preclude multithreading

Note

MySQLs default distribution format is a binary release linked with the option static. Such linking helps ensure that the administrator need not worry about system library versions. 239

A program linked with the static option is slightly bigger than a dynamically linked executable, but it is also slightly fasteran estimated 3 to 5 percent faster. However, a statically linked MySQL executable presents a problem in that it will not accept user−defined functions (UDFs). If you plan to use such C or C++ add−ins with MySQL, you must compile the application yourself, using dynamic linking.
.gz distribution files

Dealing with the GNU analog to zipped files means taking the steps below. 1. Pick the directory under which you want to unpack the distribution. Note Make sure you have both read and write privileges for the directory you choose. 2. If youre not already there, move to that directory by using the command cd. 3. Get a MySQL source distribution file from one of MySQLs Internet sites. These files exist as compressed tar archives, and have names such as mysql−VERSION.tar.gz, where VERSION is, of course, a version number. 4. Unpack the distribution into the current directory with a command similar to this:
$ gunzip < mysql−VERSION.tar.gz | tar xvf −

Such a command creates a directory named mysql−VERSION as it unpacks the distribution file. 5. Change to the top−level directory of the unpacked distribution, with a command similar to this:
$ cd mysql−VERSION

6. Configure the release and compile everything, with commands similar to these:
$ ./configure −−prefix=/usr/local/mysql $ make

When you configure MySQL, you can simultaneously specify configuration and runtime options. Run ./configure −−help for a list of such options. 7. Complete the installation with this command:
$ make install

Note

8. If youve not previously installed MySQL, create grant tables for it with a command similar to this:
$ scripts/mysql_install_db

9. After installation completes, initialize and test your database by starting the MySQL server with a command like the one below. In this sample command, the parameter BINDIR represents the directory in which the MySQL server has been installed, called in this example, safe_mysqld; the default value for this parameter and for that directory is /usr/local/bin.
$ BINDIR/safe_mysqld &

Tip If you recognized the name safe_mysqld as representing a daemon process, give yourself a few extra points, and reflect for a moment on the fact that it makes sense to run the MySQL or any other Linux database server as a daemon. Whats more, in the circumstances just cited, note that starting this daemon should not fail unless another MySQL server was already running.
RPM (Red Hat Package Manager) distribution files

If your MySQL source distribution exists as an RPM file, you must run the following command before beginning the installation and testing sequence just outlined. Carrying out this command creates a binary RPM file that you can then install:

240

$ rpm −−rebuild MySQL−VERSION.src.rpm Compiling and linking

Should you compile and link MySQL yourself, the way in which you do so affects its speed and overall performance. This section lists what I feel to be the most important aspects of MySQLs configuration. MySQL uses LinuxThreads on Linux. If you are using an old Linux version that doesnt have glibc2, you must install LinuxThreads before trying to compile MySQL. LinuxThreads can be obtained from www.mysql.com/Downloads/Linux. If you compile the MySQL server yourself rather than using the make and other installation files cited in the previous section, you can create a server which will run 10 to 30 percent faster if you use a C compiler such as pgcc or the Cygnus CodeFusion compiler. Youll create a faster MySQL executable if you link with the option static.
Compiling and configuring for multiple MySQL servers

Should you need or want to run more than one MySQL server simultaneously from the same machine, there are specific steps you must take. Tip You can determine sockets and ports used by currently executing MySQL servers with this command.

$ mysqladmin −h hostname −−port=port_number variables

Tip If a MySQL server is running on the port whose number you supplied, this command displays several important configuration variables for that server, including the socket name. You also need to edit any initialization scripts that youre using to start and/or kill MySQL servers automatically, to take into account the fact that there is now more than one such server. You dont have to recompile a new MySQL server just to start with a different port and socket. You can change the port and socket to be used by specifying them at runtime as options to safe_mysqld, with a command similar to this.
$ /full/path/name/of/safe_mysqld −−socket=file_name −−port=port_number

Implementing multiple database servers to manipulate the same database is a potentially dangerous step, especially if your operating system platform doesnt support fault−free file locking. Much preferable is configuring subsequent database servers to use their own individual database directories, with the safe_mysgld runtime option:
−−datadir=/full/path/name/of/the/directory/to be used by/safe_mysqld

Creating Multiple Database Servers Here is one example of when you might want to create multiple database servers on the same platform: the need to test a new DBMS release while leaving an existing production implementation undisturbed. Another example: an Internet service provider (ISP)s need to provide unique database server implementations for a number of customers.

241

Running multiple simultaneous MySQL servers begins with compiling those servers to use distinct TCP/IP ports and sockets in order to ensure that each server listens to the appropriate conversation, that is, receives and responds to only those requests made by its own clients. I begin by assuming that one MySQL server already exists and has been configured to use the default TCP/IP port and socket. That being true, you would then use something similar to the following multipart command.

In such a command, the parameters port_number and file_name must differ from the default values presented to the previously implemented MySQL server. Furthermore, the parameter prefix should define a directory different than the one under which the existing MySQL installation lives.

PostgreSQL This section discusses specific steps needed to install and configure PostgreSQL. Tip As was the case with MySQL, a complete list of PostgreSQL configuration parameters can be displayed with the command:

$ ./configure −−help Basic installation

Table 9−6 summarizes important PostgreSQL configuration parameters.

Table 9−6: PostgreSQL Configuration Options This Option −−prefix=PREFIX Allows You to install architecture−independent files in PREFIX; default is /usr/local/pgsql −−bindir=DIR install user executables in DIR; default is EPREFIX/bin −−libdir=DIR install object code libraries in DIR; default is EPREFIX/lib −−includedir=DIR install C header files in DIR; default is PREFIX/include −−mandir=DIR install man documentation in DIR; default is PREFIX/man −−disable−FEATURE not include FEATURE in compiled PostgreSQL −−enable−FEATURE[=ARG] include FEATURE [ARG=yes] −−with−PACKAGE[=ARG] use PACKAGE [ARG=yes] −−without−PACKAGE not use PACKAGE −−enable and −−with options specify the location of libraries to be included in the compilation, by recognized using the syntax −−with−includes=dirs look for header files for tcl/tk, and specify the location of tcl/tk header files that might be needed for the so on, in DIRS compilation, by using the syntax −−with−libraries=dirs look for additional libraries in DIRS specify the location of Perl libraries that might be needed for the compilation, by using the syntax −−with−perl build Perl interface and plperl create an interface to Perl modules by using the syntax −−with−odbc 242

Figure 9−8: A default PostgreSQL file structure As was the case with MySQL, installing PostgreSQL begins with obtaining the binary PostgreSQL distribution, in this case from ftp.postgresql.org. Once in hand, you must unpack, and begin to distribute the contents of, this compressed tar file with the following commands.
$ gunzip postgresql−7.0.tar.gz $ tar −xf postgresql−7.0.tar $ mv postgresql−7.0 /usr/src

Your next step is to build PostgreSQL with a make. Building PostgreSQL requires GNU make; no other form of this utility will do the job. To test for GNU make type this command:
$ gmake −−version

If it turns out that you must obtain GNU make, you can do so from ftp://ftp.gnu.org. Before you begin the make, ensure that you have sufficient disk space. PostgreSQL needs: • About 30MB for the source file tree during compilation • About another 5MB for the installation directory • About 1MB for the initial empty database • About 20MB should you want or need to run regression tests on the database at some point Use this command to check for the amount of disk space available to PostgreSQL:
$ df −k

Then take these steps to install the application. 1. Create the PostgreSQL superuser account under which the server will run. 2. Configure the PostgreSQL source for your system. During this step, you can specify the installation path for the build process and make choices about what gets installed. 3. Change to the src subdirectory and enter this command:

243

$ ./configure

At this point, you can include any options you want to configure into PostgreSQL. 4. Compile the server with this command:
$ gmake

Note The compilation process can take anywhere from 10 to 60 minutes. Assuming that the compile completed without error, you can run the regression test suite to verify that PostgreSQL will function according to specs on your server. Tip The Administrators Guide should probably be your first reading if you are completely new to PostgreSQL, as it contains information about how to set up database users and authentication.
Configuring automatic startup at boot time

While the PostgreSQL server can be run successfully from nonprivileged accounts without root intervention, it may nonetheless be convenient or more secure to configure it to start automatically at bootup. Most Intel UNIX systems have a file called either:
/etc/rc.local

or
/etc/rc.d/rc.local

in which the commands needed to accomplish autostart should be placed. Caution postmaster, that is, the PostgreSQL server, must be run by the PostgreSQL superuser (postgres) and not by the OS root, or any other, user. Table 9−7 summarizes operating system−specific commands to automate starting the PostgreSQL server.

To fully test your PostgreSQL implementation, create a test database with which you can tinker. Use this command:
$ createdb testdb

Then connect to that database with this command:
$ psql testdb

In response, youll receive the PostgreSQL prompt from which you can enter SQL commands and otherwise experiment. Oracle8i Of the databases with which I worked while preparing this book, Oracle8i for Linux is perhaps the most sophisticated, and certainly the most complex, making demands of and interacting with its OS platform in ways that neither MySQL nor PostgreSQL do. So, I begin the discussion of Oracle8i with a summary of its most significant requirements (Table 9−8).

Table 9−8: What Oracle8i Needs from Linux Category Linux Kernel Factor SHMMAX SHMMIN SHMMNI Description What Oracle8i Considers a Default maximum allowed value 4294967295 Parameters for shared memory minimum allowed value 1 for shared memory maximum number of 100 shared memory segments allowed maximum number of 10 shared memory segments to which a user process can attach maximum amount of shared memory that can be allocated systemwide number of semaphores 200 allowed number of semaphore 70 set identifiers in the 245

SHMSEG

SHMMNS

SEMMNS SEMMNI

system; SEMMNI determines the number of semaphore sets that can be created at any one time Linux Kernel SEMMSL maximum number of Equal to or greater than the value of Parameters semaphores that can be the PROCESSES initialization in one semaphore set parameter; should also equal the maximum number of Oracle processes Mount Points At least four mount points, all at the same level of the directory structure; one is for the software, three are for an OFA−compliant database OS Groups OSDBA database administrator dba for Oracle OSOPER database operator; may oper exist as own group or as a user who is a member of the OSDBA group OS Account dedicated solely to installing and upgrading the Oracle system; the account must be a member of the group used by OSDBA Oracle bin directory for software /usr/local/bin Directory shared among Oracle users oratab file information about Oracle instances file masks use OS command umask creates file access permission 022 Environment DISPLAY machine name and Variables monitor of the station from which you are connectingto the server Oracle Corporation recommends that you do not include /usr/ucblib in your LD_LIBRARY_PATH. If you require /usr/ucblib in LD_LIBRARY_PATH, make sure it appears after /usr/ccs/lib in the search order Environment LD_LIBRARY_PATH needed by Oracle must include $ORACLE_HOME/lib. Variables products using shared libraries ORACLE_TERM required by all character mode and Motif mode Oracle products ORACLE_SID specifies the instance name, or server ID 246

(SID) of the Oracle Server; must be unique for each Oracle instance running on a given machine; Oracle Corporation recommends using four characters or fewer ORACLE_HOME set to the directory where the Oracle software will be installed; recommended: $ORACLE_BASE/product/release recommended: software_mount_ point/app/oracle must include all of: $ORACLE_HOME/ bin /bin /usr/bin /usr/local/bin directory housing source unidentified at install; if SRCHOME code is set, the Installer defaults to the location it specifies to find software to install an alternate database for should be undefined at Install; If you certain objects set TWO_TASK and are creating database objects, the Installer attempts to place them in the database specified by TWO_TASK. A directory with at least 20MB of available space where the Oracle account has write permission; the default location on Linux is /usr/tmp

ORACLE_BASE

PATH

the directory at the top of the Oracle file structure search path

SRCHOME

TWO_TASK

TMPDIR

Tasks that must be carried out as the root user

This section outlines the half−dozen steps that must be taken by the superuser to configure the operating system to accept Oracle8i. 1. 1. Configure Linux kernel for Oracle. Set Linux kernel Interprocess Communication (IPC) parameters to accommodate the shared memory required by the Oracle8i Server. (You wont be able to start this server if the system hasnt been configured with enough shared memory.) Type the command:
# ipcs

to display the operating systems current shared memory and semaphore segments. Then set the kernel parameters listed below as defined in Table 9−8. 247

♦ Maximum size of a shared memory segment (SHMMAX) ♦ Maximum number of shared memory segments in the system (SHMMNI) ♦ Maximum number of shared memory segments a user process can attach (SHMSEG) ♦ Maximum amount of shared memory that can be allocated system−wide (SHMMNS) 2. 2. Create mount points. An Oracle8i Server must have at least four mount pointsone for the DBMS software, and at least three more for database files. All such mount point names, whatever their use, should follow the pattern /pm, where p is a string constant and m is a fixed−length key to distinguish between mount points. 3. 3. Create OS groups for database administrators. The Oracle Installer assigns database administrator and operator privileges to operating system user groups during installation, calling these categories of privileges OSDBA and OSOPER, respectively. Members of the groups to which these privileges are assigned these groups automatically, therefore, have the corresponding privileges under Oracle. So, the groups you wish to use for these roles must exist before you start the Installer. On most Intel UNIX platforms, use a command of this type to create such groups if they do not already exist.
# grpadd oracledba oracleoper

4. 4. Create an OS account to own Oracle software. Because the operating system user account youve set up for oracle itself owns the Oracle distribution, you must run the Installer under this account. Therefore, you must first ensure that the account exists and is defined appropriately. Under most Intel Linux operating systems, the utility useradd allows you easily to create this or any other user account. Follow the specifications set out in Table 9−9 for the oracle user account.

Table 9−9: Characteristics of the oracle User Account Value Can be anything, but make it mnemonic, for example, oracle. Default Group Identification (GID) Can be anything, but make it mnemonic, for example, OSDBA or OPER as appropriate. Home Directory Choose a home directory consistent with other user home directories. Note also that the home directory of the oracle account should not share the same value as the ORACLE_HOME directory. Login Shell Can be the Bourne shell (/bin/sh), the C shell (/bin/csh), or the Korn shell (/bin/ksh). Tip Sites with multiple Oracle servers may install them under the same oracle account or under separate accounts. If multiple installations share an oracle account, the DBAs for each installation have access to the other installations. If this presents security problems, install each Oracle system under a different oracle account. 5. Create a local bin directory. With Oracle, as is true of all software, a common environment expedites administration. Such an environment should include a database−specific bin directory for shared software, which is outside the ORACLE_HOME directory. To create this common environment, take these steps. a. Create a local bin directory, such as /usr/local/bin, with commands similar to these. (Of course, the exact nature of your file systems structure will dictate the precise parameters you must supply to such commands.) 248 Parameter Login Name

and updating the environment. Use the syntax shown below as appropriate to your shell to set the environment variables outlined above in Table 9−8. use a command of this pattern:
setenv variable_name value
Because there are so many possible values for this environment variable. other than the owner of a file. 2. c. use the following command to set masks to that value:
umask 022
This command ensures that all users on a system. Set new file permissions. contains information about Oracle instances. Copy the oraenv (or coraenv under the C shell) and dbhome configuration scripts to the newly created local bin directory. For the Bourne shell. but not write to. ORACLE_TERM identifies the terminal definition resource file to be used with the Installer. and that those users have execute permissions on the directory. Therefore. However. default permissions assigned to files at their creation.
Table 9−10: Typical ORACLE_TERM Settings Terminal Type 249 ORACLE_TERM Setting
. Create the oratab file. you must run the script cdrom_mount_point/orainst/oratab. that is. they have a table of their ownTable 9−10. newly created files. simply type:
umask
If the OS reports anything other than a value of 022. individual Oracle sessions. To check existing file masks. setting environment variables. Use the umask command both to check and to set file masks. enter commands whose syntax follows this pattern:
variable_name=value export variable_name
For the C shell.
Tasks that must be carried out as the user oracle
A number of Oracle configuration tasks can be carried out from a login to the oracle account. Ensure that this newly created directory appears as part of the PATH of every user who must work with Oracle. 1. that is. These include setting permissions for newly created files. including those the Oracle Installer creates. the oratab file. The oracle user account owns oratab.sh in order to manipulate the /etc directory appropriately. An important Oracle8i administrative file. the file lives in a directory that requires root privileges. when creating the file or setting permissions on it. Set environment variables. You can also copy or move other software that you want all users to be able to access to this directory.# # # #
cd /usr mkdir local cd local mkdir bin
b. can read and execute. 1. 6.

Make the newly created mount point directory readable. you can immediately update the environment so that the current. 1.profile
For the C shell. and executable for all users with a command similar to this. type this command:
$ source . Update the environment. Log in as the root user and create a CD−ROM mount point directory. with a command of this pattern:
# mkdir cdrom_mount_point_directory
3. Caution Preclude damage to the CD or the drive by unmounting the medium before removing it from that drive. writable. active shell session reflects the characteristics just specified. Mount the CD−ROM drive on the mount point directory and exit the root account.login Running the Oracle Installer
The Oracle Product Installation CD−ROM is in RockRidge format.login as appropriate to your shell. you must have root privileges to mount or unmount the CD−ROM.profile or .
# mkdir /cd # chmod 777 /cdrom
250
. Of course./.
Take these steps to prepare to run the Oracle Installer.
chmod 777 cdrom_mount_point_directory
4. use this command:
$ . For the Bourne or Korn shell. Once youve properly defined all environment variables in . Place the Product Installation CD−ROM in the CD−ROM drive. 2. with commands such as these:
# mount options device_name cdrom_mount_point_directory # exit
A more specific Linux example might use this syntax.AT386 console 386 AT386 xterm 386x UnixWare terminal 386u Solaris x86 xterm 386s Data General 200 dgd2 Data General 400 dgd4 IBM High Function Terminal and aixterm (color) hftc IBM High Function Terminal and aixter hft (monochrome) hpterm terminal and HP 700/9x terminal hpterm IBM 3151 terminal 3151 vt220 terminal vt220 3.

creating control files.
Installation log files
The Oracle Installer creates four log files in which it records the current installation sessions activities. thereby building a database. Table 9−11 describes some navigational details of working with the Installer.
Table 9−11: Navigating Within the Oracle Installer Keystroke Tab key Arrow keys Spacebar Tip Action Produced Move to next block Move between fields Selects current fields The Installer can record responses from one installation session. and then apply those to subsequent installations. ♦ Issue commands of the following patterns. each displayed in its own window. you cannot use the default installation path. the Installer will display and ask you to confirm the settings it plans to use. $ .
$ cd cdrom_ mount_point_directory/orainst. and thereby possibly deny access to others. Doing so would assign file ownerships and permissions appropriate to that user. These logs store information regarding: • The Installers manipulation of the operating system • The Installers own activities • Activities related to Oracle SQL • Activities related to installation makefiles If you accept the default presented by the Installer at this point./orainst
Caution Do not run the Installer as the root user. Tip The default path assumes that you are installing from CD−ROM. in what Oracle calls silent mode.old before creating the current log set. andperhaps most importantsaving the time that would otherwise be needed to load and run data dictionary creation scripts. If you decide upon both a default installation and the simultaneous creation of a database.# mount −t iso9660 /dev/cdrom /cd # exit
5. Start the Installer with these steps: ♦ Log in as oracle user.
Installer screens
An Oracle Installer session consists of a series of prompts. The first such window enables you to choose a default or a custom installation. enabling them to be carried out noninteractively. all of these logs will be placed in the directory $ORACLE_HOME/orainst. If you are installing from a network drive or from some other form of what Oracle refers to as a staging area. If you simply choose a default installation. 251
. the Installer copies prebuilt data files to the specified mount points. the Installer will first rename them as xxx. Should earlier versions of the logs exist.

monitors the storage required by the DBMS features you select.S.sh. no separate user group will receive operator privileges. Be aware. is. English. Note also that the Installer itself operates only in U. Therefore. defined in the environment variable ORACLE_SID. as you choose what you want to install from the Asset Managers Available Products window.
Instance name
An Oracle8i instance name. simply double−click the name. Tell the Installer to create a new file. comparing that to space available in the destination ORACLE_HOME directory.sh. this parameter defaults to the primary user group of the oracle account. youll be prompted a second time.
National language support
Should you need to use a language other than U. you should supply an instance name that is not only a unique identifier. must be run by the root user after installation. This parameter defaults to the group you specified as the OSDBA group. because the Installer deletes temporary staging areas as it installs.
The root. the Installer displays choices available for the user group that will be granted Oracle DBA privileges.
252
. To expand a category name to reveal its component products.
OSOPER group
As it did for the database administrator. you might receive further Installer prompts pertaining to available disk space.S. the Installer prompts you to choose a group which will be granted Oracle OPERATOR privileges.
OSDBA group
In its next prompt screen. it will prompt you to learn whether it should append new actions to it. but also no more than four characters long. or to create a new root. Tip The Software Asset Manager groups many products under categories such as Protocol Adapters or Precompilers. select it and press Enter. Should you go along with this default. you can specify it with this prompt screen. If the Installer detects a previous copy of this script.
Software asset manager
Oracles Installer tool. In other scenarios. to specify whether the staging area is temporary or permanent. called Software Asset Manager. that this default language can be overridden by settings supplied by users or even client applications when a session is initiated. If you indicate the latter. and denotes these categories with a plus sign to the left of the name.sh script
The script root. Oracles default administrator group. the Installer will accept your choice but have to relink the DBMS executable. English for messages from Oracle8i.Install source
The next Installer prompt window asks you whether you are installing from CD−ROM or from a staging area. though. Or. If you do choose a group other than dba. in single−database installations. in character mode. created by the Installer in the $ORACLE_HOME/orainst directory. supplied the same value as the DB_NAME initialization parameter.

A nondefault character set cannot be changed without recreating the database it affects. follow the recommendation of Oracle Corporation to spread your database across at least three independent devices.
National character set
The national character set for which the Installer next prompts you affects only specially declared columns. Table 9−12 summarizes the default size and placement for the sample or demonstration database the Installer will create.
Mount point Locators
Oracle Corporation recommends that the database mount points you specify in this window differ from the software mount point you defined to the initial Installer prompt.
253
. the default is US7ASCII.dbf
This Installer prompt screen enables you to specify the character set in which the database will be stored. control and redo log files are also spread across the mount points you specify.dbf db_mount_point1/oradata/ db_name/users01.Database creation
The following prompts appear only if you use the Installer to create a database. When you accept this default in the Number of Mount Points prompt screen.
Number of mount points
When installing the Oracle8i server. Use this screen to supply passwords for both these accounts that are appropriate for your environment.dbf db_mount_point1/oradata/ db_name/rbs01.dbf db_mount_point1/oradata/ db_name/temp01.
SYS and SYSTEM user passwords
The Installer prompt screen for the Oracle8i (as opposed to operating system) user accounts SYSTEM and SYS shows defaults of manager and change_on_install respectively.dbf db_mount_point1/oradata/ db_name/tools01.
Table 9−12: Sample Database Summary File Control Files Redo Log Files SYSTEM ROLLBACK TEMP USERS TOOLS
Character set
Default Size 50KB 500KB 80MB 15MB 550KB 1MB 25MB
Minimum Size database−dependent 100KB 5MB 1MB 260KB 200KB 1MB
Default Location db_mount_point[1−3]/ oradata/db_name/ control0[1−3].log db_mount_point1/oradata/ db_name/system01. it defaults to the character set you specified as the database character set.ctl db_mount_point[1−3]/ oradata/db_name/ redosid0[1−3]. To choose any character set other than the default requires having set the environment variable ORA_NLS33 during preinstallation to a matching value. Change this only after careful consideration.

Multithreaded server
Configuring the Oracle8i server to act as a Multithreaded Server (MTS) allows you to keep to a minimum the number of processes and amount of memory certain types of database applications will demand. Set these passwords. Oracle Corporation considers MTS best suited for systems running applications with few long−running transactions. and therefore requires a separate Installer session to be loaded. in addition to whatever other products you wish to load. with the latter type sometimes referred to as generic. Product documentation. However./root.sh
254
. simply choose Linux Documentation.
Tasks to perform as the root user
To begin configuring Oracle8i.
Verifying the Installers work
After installation completes. and performs other configuration activities. because doing so enables authentication on attempts to connect to the Oracle8i server as either user. such as Oracle InterOffice. On the other hand.
The root. To install operating system−specific documentation.sh script
Running the root. Run this script with commands similar to these:
# cd $ORACLE_HOME/orainst # . The distribution CD houses operating system−specific documentation.
Installing documentation
Oracle documentation can be either operating system−specific or product−related. occupies its own CD−ROM. on the other hand. the Oracle8i Installer automatically returns to the Software Asset Manager screen from which you can verify that all products selected show as having been installed. After completing an Installer session. thereby allowing this document category to be installed during the overall software installation. Then carry out the tasks described in this section.The dba and operator group passwords
Next. the Installer asks whether you want to set passwords for the operating system user groups to whom you granted database administrator and operator privileges. Keep these caveats in mind when responding to this Installer prompt. from the list of available products presented to you at the early stages of the installation. such as those found in decision−support applications. both categories of Oracle8i documentation are provided in both HTML and PDF formats.sh script created by the Installer in the $ORACLE_HOME/orainst directory sets file permissions for Oracle products. Oracle considers MTS not well suited for systems supporting long−running transactions. certain configuration tasks must still be done. log in to the operating system as root.
Configuring Oracle8i
Completing installation doesnt mean youve also completed setting up Oracle8i.

Change the value for every database whose launching and closing you wish not only to automate but to link to operating system startup to Y. 3. but strongly recommends automating the capability to shut down the DBMS as a means of protecting the suite from errors or corruption caused by improper shutdown. and sid3. write. and may also prompt for such parameters as usernames.
Create additional Linux accounts
Should more than one user of your system need to exercise database administrative privileges. dbshut and dbstart. As Oracle Corporation points out in its Administrators Guide.
Table 9−13: Oracle File Security Area of the DBMS All common system files and installation files All common system files and installation files Any files or directories in an Oracle installation
Automate database startup and shutdown (optional)
Recommended Characteristics Owned by the user account oracle Should provide read.sh informs you of its progress as it works.d/init. Set up dbstart and dbshut to be called at bootup by taking these steps: 1.
Verify database file security
Ensure that your newly installed DBMS adheres to the file modes and ownerships recommended by Oracle Corporation. you cannot have dbstart automatically fire up databases sid1. pertain to the same database or set of databases. Two scripts. found in the $ORACLE_HOME/orainst directory.
The catrep. and execute privileges to all members of the OSDBA user group Should not provide write access to any user not a member of the OSDBA user group
Oracle Corporation considers automating database startup optional. automate database shutdown and startup. respectively. you must run the script catrep. but have dbshut close only sid1 and sid2. each such user must have his or her own account affiliated with the OSDBA user group. Table 9−13 outlines these modes and ownerships.sh will ask you to confirm the environment before it performs any actions.root. thus allowing you to terminate the script should you need to reset anything in the environment. but you do not need to rerun the Installer. create a file called dbora in the directory /etc/rc.sql script
If youre installing Oracle8i for the first time. Edit the file /etc/oratab. to give the DBMS the capability to replicate. therefore. Any additional such accounts that are needed should be created at this point with the utility useradd. you must rerun it. At the end of the file dbora. place entries similar to those shown in the example below. whose entries take the format:
ORACLE_SID:ORACLE_HOME:{Y|N}
where Y or N specify respectively using or not using dbstart and dbshut to start up and shut down the database. found in the $ORACLE_HOME/bin directory. sid2. If it doesnt already exist. root. If you terminate the script. Both scripts reference the same records in the oratab file. Be sure to use 255
.sql. and must. 2.

d/dbora /etc/rc0.d/K10dbora
After specifying startup and shutdown options..d/init. needed to install any Linux DBMS • Reviewing vendor−specific installation instructions
256
. such as chmod and groupadd. your work as root to install Oracle8i is finished. stop) # Or. ln −s /etc/rc.
# Set ORA_HOME to the location of dbshut # Set ORA_OWNER to the user id of the owner of the Oracle database ORA_HOME=/u01/app/oracle/product/8.full path names.5 ORA_OWNER=oracle # Test for the presence of the script dbstart in ORA_HOME if [! −f $ORA_HOME/bin/dbstart −o ! −d $ORA_HOME] then echo "Oracle startup: cannot start" exit fi # Assuming dbstart is in the right place case "$1" in start) # Start the Oracle databases su − $ORA_OWNER −c $ORA_HOME/bin/dbstart & . and of how much those resources might have to grow to accommodate your growing databases • Grasping and being able to use correctly the basic Linux concepts and commands. like this. which in turn requires understanding at least some of normalization theory • Having a clear picture of your intended platforms resources. stop the Oracle databases in background after becoming the user ORA_OWNER su − $ORA_OWNER −c $ORA_HOME/bin/dbshut & . esac # Link dbora to operating system startup with a command appropriate to # your environment..0.
Summary
Getting ready for any Linux DBMS means: • Understanding and using effective schema design.

and field names.Chapter 10: Interacting with the Database
As a Linux database administrator. import text into a MySQL database in order to populate its tables. This section discusses three commonplace.
# mysqldump [OPTIONS] database [tables] # mysqldump [OPTIONS] −−databases [OPTIONS] DB1 [DB2 DB3] # mysqldump [OPTIONS] −−all−databases [OPTIONS]
Table 10−1 summarizes this syntax. assumes both client and server support compression 258 Syntax # mysqldump [OPTIONS] database [tables] # mysqldump [OPTIONS] −−databases
. according to the options given if any Dumps out the contents of the specified [OPTIONS] DB1 [DB2 DB3] databases. Such dumps can include the MySQL statements needed to create or populate the tables involved. operations: • Dumping a database • Importing text files into a database • Displaying database summary information
Interacting with MySQL
MySQL offers command−line utilities by means of which you can dump the contents of one or more databases. you will need to interact with your DBMS in a number of ways. mysqldump will output everything in every database. and display database.
Table 10−1: mysqldump Syntax Effect Dumps out the contents of the specified database and tables. provides faster inserts • mysqldump A or mysqldump −−all−databasesDump all databases • mysqldump −−allow−keywordsCreate column names that include keywords. [OPTIONS] according to −−all−databases the options given if any Caution If you dont supply table names or use the −−databases or −−all−databases options. table. • mysqldump −−add−locksLocks tables before and unlocks tables after each table dump.
Dumping a database
You must use the utility mysqldump to dump one or more MySQL databases in order to back them up or to transfer them to another MySQL server. according to the options given if any # mysqldump [OPTIONS] Dumps out the contents of all databases. but still essential. The three commands below are each examples of generalized syntax for the mysqldump utility. functions by causing mysqldump to begin each column name with the appropriate table name • mysqldump C or mysqldump compressCompress all information that passes between client and server. Heres a lineup of what I consider to be the most useful of mysqldumps options.

dumps directly to standard output • mysqldump −u user name or mysqldump −−user=user nameConnects to the MySQL server as the indicated user before doing the dump. you must first rename the text file to comestibles. Table 10−2 summarizes the most useful of mysqlimports options. Remove all existing data from a table before importing text file Ignore errors such as those generated by a text file not having a corresponding. Causes mysqlimport to attempt to continue the import beginning with the next text file available. and uses the result to decide which table in the indicated database will receive the text files contents. with syntax like this:
mysqldump −−database_of_gardening −−where=plant_name=zinnia | mysql −−host=far_away_machine
Importing text files
The command−line interface to MySQLs LOAD DATA statement is mysqlimport. whose single quotes are required
Tip One can use the where option of mysqldump to do an ad hoc display of records sharing a specific characteristic. if any.• mysqwldump B or mysqldump databasesDumps several databases. Most of the options that this utility accepts are identical to those of that statement. useful when only a dump of the structure of a table is needed • mysqldump ppassword or mysqldump −−password=passwordConnects to the mysql server with the permissions associated with the supplied password before beginning the dump • mysqldump q or mysqldump quickCarries out dump without buffering.
Table 10−2: mysqlimport Options Option −C or compress −d or delete −f or force Effect Compress all information as it moves between client and server.txt into a table called comestibles in a gardening database.
# mysqlimport [options] database ASCII file 1 [ASCII file 2] [ASCII file 3]
Caution Be careful in naming. without the need to supply table names.txt. The utility mysqlimport strips off any extension from the name of a file to be imported. or deciding upon. default for usernameoperating system login name of current user • mysqldump w or mysqldump −−where="condition"Dumps only those records specified by the condition stated in the where clause. wh transferring those records to another MySQL database. files that mysqlimport may have to work with. Launch mysqlimport with a command of this general syntax. assumes that both support compression. Without this option. So. if you want to import data from a file called veggies. mysqlimport will place the results of the importing in a new table called veggies. Otherwise. mysqlimport will exit if a table doesnt exist to receive the 259
. because all arguments are regarded as database names • mysqldump F or mysqldump −−flush−logsFlush all MySQL log files before starting the dump • mysqldump f or mysqldump forceComplete the dump even if SQL errors occur during the dump • mysqldump h or mysqldump −−host= named hostDump from the active MySQL server to the named host. the default value for the named host parameter is localhost • mysqldump l or mysqldump −−lock−tablesLock all tables before beginning the dump • mysqldump d or mysqldump −−no−dataWrite no row information. pre−existing table in a database.

Kirk Constable Odo
Command Fragment mysql e
an inquiry of the newly created and loaded table might look like this. end the MySQL session. −r or −−replace Replace existing rows whose key fields have unique values duplicated in input records with those input records. MySQLs response to these commands is in italics. Table 10−3. that is. −h host_name or Import data to the MySQL server on the host indicated by −−host=host name the host name parameter. preclude any write operations to those tables. −i or ignore Ignore. Again. input records whose key fields values duplicate those of existing records. The code sample below demonstrates mysqlimport.txt look like this:
001 002 Captain James T. MySQLs output from the command you enter is italicized. name Create a new table called trek_good_guys. and then quit. Such a file can be created in any of the editors Intel UNIX makes available. CREATE TABLE trek_good_guys (id INT. −l or −−lock−tables Lock ALL tables. trek_trivia Create the indicated table and fields in the new database called trek_trivia. that those tables are synchronized. VARCHAR(25)) define two fields for that table: an integer field called id and a variable−length character field called name.txt. before importing text files. elaborates upon it.txt to the database called trek_trivia from the ASCII file called trek_good_guys. that is.
$ mysql −e SELECT * FROM trek_good_guys trek_trivia +−−−−−−+−−−−−−−−−−−−−−−+
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.txt trek_trivia. Therefore ensures that all tables on the server contain the same data.contents of a text file. that is. This option is needed if you wish to override mysqlimports default behavior of obtaining text files from the MySQL server on the default host.
$ mysql −e CREATE TABLE trek_good_guys(id INT. from the active MySQL client. that is. whose maximum length can be no more than 25 characters. which follows this sample. name VARCHAR(20)) trek_trivia $ mysqlimport −−local trek_trivia trek_good_guys. that is. mysqlimport local Import data from the local host trek_trivia trek_good_guys. Assuming that the contents of trek_good_guys. execute the command encased in single quotes. that is do not import. on the machine specified by the OS parameter localhost. −L or local Get input files locally. after first using mysql itself to create an empty database and table into which the contents of a text file can be placed.trek_good_guys: Records: 2 Deleted: 0 Skipped: 0 Warnings: 0
Table 10−3: Understanding mysqlimport Means Start MySQL. Finally. Further.

mysqlshow will display information only on databases. However. that look may vary slightly depending upon such OS characteristics as terminal definitions.
Interacting with PostgreSQL
This section reviews the PostgreSQL utilities that enable you to dump the contents of one or more databases. tables. functions. information on all matching columns and column types in the indicated or in all tables will be displayed Note also that in the most recent versions of MySQL. and of those tables columns or fields. pg_dump generates queries that re−create all user−defined types. pg_dump copies out all data as text so that it can be copied in again easily or even dumped into a text editor for further massaging. 261
. aggregates. import text as data for a database. and that can be used to reconstruct the database on the local or some other host). if you do not supply a: • Database name to mysqlshow. More specifically. and operators. a file that is in ASCII form. information on all matching databases will be displayed • Table name to mysqlshow. tables.| id | name | +−−−−−−+−−−−−−−−−−−−−−−+ | 001 | Captain James T. information on all matching tables in the indicated or in all databases will be displayed • Column name to mysqlshow. Finally. Invoke mysqlshow with generalized syntax similar to this:
$ mysqlshow [OPTIONS] [database [table [column]]]
Watch Out for Whats Missing Be aware that. pg_dump pg_dump places the contents of a PostgreSQL database into a script file (that is.
Displaying database summary information
The command−line utility mysqlshow gives a thumbnail sketch of existing databases and their tables. Kirk | | 002 | Constable Odo | +−−−−−−+−−−−−−−−−−−−−−−+
Tip Ive done and shall continue to do my best to reproduce both the content and the look of MySQLs responses. and display database summary information. indices. that holds query commands. and columns for which you have the necessary read privilege.
Dumping a database
PostgreSQL offers two utilities that can dump the contents of databases: pg_dump and pg_dumpall.

pg_dump [ dbname ] pg_dump [ −h host ] [ −p port ] [ −t table ] [ −a ] [ −s ] [ −u ] [ −x ] [ dbname ]
Table 10−4 describes what we consider the most useful pg_dump options. host names may also be supplied for this parameter −p port pg_dump p 2345 x trek_trivia Connects to the postmaster by means of the specified TCP/IP port or local socket file extension to which the postmaster listens. to the trek_trivia PostgreSQL server. and withholds any user− or permission−related information from the dump −h host pg_dump h 207. and not the schema. of the database trek_trivia to standard output −t table pg_dump t starships trek_trivia Dumps only the schema and data of the table starships in the database trek_trivia to standard output −u pg_dump −t starships −u Dumps only the schema and data of the trek_trivia table starships in the database trek_trivia to standard output.pg_dumps generic syntax comes in two flavors. pg_dump can write either to an ASCII file or to standard output. of the database trek_trivia to standard output −s pg_dump −s trek_trivia Dumps only the schema. on the machine indicated by the given IP address. your best bet is to ensure that you have permissions adequate to the dump. An easy way to check this is to do a simple query of the database in question from psql. 262
.
Table 10−4: pg_dump Syntax Effect or Fragment Dumps the contents and schema of the database trek_trivia to standard output −a pg_dump −a trek_trivia Dumps only the contents. after prompting for a PostgreSQL username and password −x pg_dump t starships x Dumps only the schema and data of the trek_trivia table starships in the database trek_trivia to standard output.233. as these examples demonstrate:
% pg_dump % pg_dump > trek_out
Command dbname
Example pg_dump trek_trivia
Tip Should pg_dump return errors. and withholds any user or permission related information from the dump. port number defaults to 5432 However you structure its command line. and withholds any user or permission related information from the dump.251 x Connects to the postmaster. that is.102. and not the data.

Importing text files
Just as it relies on the OS concept of redirecting output to place the results of a dump in an ASCII file. Otherwise. As a result. its syntax and behavior are identical to those of pg_dump as weve just presented them. I created a text file called trek_out with this command:
% pg_dump > trek_out
To reload this information to a new database. it dumps all existing PostgreSQL databases into a single script file. it does not recognize the arguments dbname or −t table. vacuumdbs generalized syntax in its most usable form and as it pertains to such analysis looks like this:
vacuumdb [ −−analyze | −z ] [ −−alldb | −a ] [ −−table table [ ( column [.
Table 10−5: Using vacuumdb as a Database Analysis Tool Command −z or −−analyze Example $ vacuumdb −−analyze firstdb Effect or Fragment Prepare statistics on the database firstdb that the PostgreSQL optimizer can use Analyze all databases on the local host Work only with the column classification in the table starships of the database trek_trivia Work with the database firstdb running under the postmaster on the remote machine whose host name is library Work with the database firstdb running under the postmaster that listens at the port numbered 2345 Work with the database firstdb.] ) ] ] [dbname ]
Table 10−5 elaborates on vacuumdb. Lets go back to my example of the former and enlarge upon it to illustrate the latter.out
Displaying database summary information
PostgreSQL offers the utility vacuumdb to enable you to clean or simply to analyze a PostgreSQL database. with the identity and privileges associated
−a or −−alldb $ vacuumdb −−analyze −−alldb −t or −−table table name $ vacuumdb −−analyze −−table or column name starships(classification) trek_trivia −h or −−host host name or IP address $ vacuumdb h library −−analyze firstdb
−p or −−port port number $ vacuumdb p 2345 −−analyze firstdb
−U or −−username username
$ vacuumdb U adhoc −−analyze firstdb
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. so PostgreSQL leans on the mirror−image idea of redirecting input to import the dumped information. I need only issue this command:
% psql −e next_gen < db.pg_dumpall pg_dumpall does just what its name suggests.

substituting instead the utilities EXPORT and IMPORT. Effect Create a new database Delete a database and all its tables Kill mysql clients by supplying the process ID associated with those clients. and if need be adjust.−W or −−password Tip
$ vacuumdb W −−analyze firstdb If vacuumdb returns the simple message
VACUUM
with the PostgreSQL user adhoc Work with the database firstdb.
Navigating the Server Console
This section discusses the administrative functions of using a Linux DBMS server console. in turn obtained with the command process list Use ping to determine if the daemon mysqld still runs Display a list of all active client sessions currently being serviced by mysqld Stop the MySQL server Display server status information
ping processlist shutdown status Tip
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.
its telling you something went wrong. Again. which handle data or data definitions in internal binary Oracle8i format.
MySQL
Every MySQL server relies on the utility mysqladmin to carry out all management of the DBMS. after prompting for a PostgreSQL password
its telling you it had no problems. The generalized syntax for this utility is:
# mysqladmin [OPTIONS] command [command−option] command
Table 10−6 summarizes the most useful commands that you can pair with mysqladmin. If. it displays something similar to
vacuumdb: Vacuum failed. table. substituting instead a number of GUI−based monitoring capabilities. • A command−driven means of obtaining summary statistics for any level of a database. and column permissions. however.id.
Table 10−6: mysqladmin Commands Command create databasename drop databasename kill id.
Interacting with Oracle8i
Despite being such a formidable DBMS. the database. Oracle8i lacks two major features: • The capability to dump either data or schema into an ASCII file. your best debugging bet is to check.

Note that because MySQL implements databases as directories. mysqladmin stat would produce the same output as mysqladmin status. tables. the number of flush. the number of seconds the MySQL server has been running • Threads. mysqld • Slow queries. CREATE DATABASE creates only a directory under the MySQL data directory. a . similar to Memory in use. and an . For instance. queries whose execution has needed more than a predefined number of seconds • Opens. Status information available under mysqladmin includes: • Uptime. Deletes the database pittsburgh_pirates if that database exists. normally.frm file. that is. the number of queries from clients since the most ercent launching of the MySQL server or daemon. that is. that is. that is. that is. in that created directory. and only available when the MySQL server was started with the option −−with−debug • Max memory used.
drop databasename
mysqladmin DROP DATABASE IF EXISTS pittsburgh_pirates
kill id
mysqladmin kill 3456
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. that is. DROP DATABASE returns the number of files that were removed. contain files corresponding to tables in the database. the maximum memory mysqld can allocate.MYI. that is. this value is three times the number of tables in the database. which. the number of tables currently open • Memory in use.
Table 10−7: Examples of mysqladmin Commands Command create databasename Example mysqladmin CREATE DATABASE IF NOT EXISTS pittsburgh_pirates Result Creates the empty database pittsburgh_pirates if that database does not already exist. and/or reload commands that have been carried out since mysqld was most recently started • Open tables. the number of active clients • Questions.MYD. that is. It does not place any files. that is. memory allocated directly by mysqld. in turn. how many tables are currently open under mysqld • Flush tables. Max memory used is only available when the MySQL server was started with the option −−with−debug Output from mysqladmin stat might look similar to this:
Uptime: 10077 Threads: 1 Questions: 9 Slow queries: 0 Opens: 6 Flush tables: 1
Open table
Table 10−7 gives examples of the mysqladmin commands Ive discussed. refresh. because each table is represented by a . Terminates the client session whose process ID is 3456. that is.All the commands described in Table 10−6 can be abbreviated.

or delete • Save queries as views • Save table definitions • Save view layouts • Save preferences. for exa
• Open multiple tables for viewing. or visit the PostgreSQL Web site at: www.ping
mysqladmin u root ping
processlist shutdown status
mysqladmin proc mysqladmin shut mysqladmin stat
Temporarily takes on the identity of the root user before pinging the MySQL daemon.
PostgreSQL
PostgreSQL. its this:
pgaccess [ database name ]
Now for the roll call of some of the more impressive of pgaccesss capabilities.
pgaccesss syntax couldnt be simpler. • Resize columns by dragging their vertical grid lines • Retrieve information such as owner. and carry out dozens of DB administration functions. define queries. when viewing query results • Execute VACUUM • Load or save reports from/to a database • Perform ad hoc queries such as
select * from starships where classification=[parameter "Please enter a starship class. and save queries with a visual tool that supports drag and drop • Call user−written scripts • Create tables through an assistant • Delete or design views • Delete records simply by pointing and then pressing the Delete key • Dynamically adjust row height when editing • Edit in place. edit. In general. This tool can: • Access record sets with a query widget • Add new records.readysetnet.pgaccessrc under the PostgreSQL file subsystem 266
. update. the list of pgaccess features is so long that I only outline the most valuable of them. offers a means of carrying out administrative tasks that its Open Source peer MySQL does not. Displays status information for the MySQL server. and more for specified tables • Run action queries such as those which insert. This GUI−based tool is called pgaccess. In fact. consult the CD−ROM that accompanies this book. in the file . field characteristics.postgresql. pgaccess enables you to manage or edit tables. Cross−Reference For specifics on or practice with pgaccess.com. Displays a list of all MySQL processes currently running. Stops the MySQL server. that is. saving them with a right−click • Build. presenting as it does so a user−configurable maximum number of records • Open user−defined forms • Open any database on any host at a specified port and under a specified username and password • Rename or delete tables. because it is so closely interwoven with languages such as Tcl/Tk.

Tip You must install Server Manager views for each database you wish to administer. Using Server Manager in graphical mode Not only Server Manager itself but also a number of views of the databases you intend to manage must be present on your machine before you can use this tool. creates these Server Manager views. because many of Server Managers windows include information selected from data dictionary tables. CATSVRMG. shutdown. Server Manager is started with this command from the OS prompt:
$ svrmgr
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. exists in both a GUI−based and a command line−based form. and is run automatically during installation. you need the SELECT ANY TABLE system privilege to fully utilize Server Managers interface. the most widely used PC desktop which is X Windows based. This section gives an overview of that tool. and Server Manager commands • In its GUI−based incarnation. An Oracle8i script. even if you implement only one copy of Server Manager. concurrently perform multiple tasks • Perform common DBMS administrative tasks such as server startup. which is included with Server Manager on the Oracle8i distribution media. Server Manager Server Manager.• Specify sort orders • Specify ad hoc filters such as
like position="Catcher"
• View the results of select queries
Oracle8i
As one might expect of such a high−powered commercial DBMS. backup. the nuances of Oracle8is administrative capabilities far outnumber those of either MySQL or PostgreSQL. Server Manager can be used to: • Administer both local and remote databases • Administer multiple databases • Dynamically execute SQL. Oracles database administration tool. check the version information in Server Managers Administration window or issue the following query:
SM$VERSION (SELECT * FROM sm$version Privileged operations
Tip
As you might expect. However.SQL. and recovery In its GUI persona.
Starting Server Manager
On most Intel UNIX platforms. To verify that appropriate Server Manager views have been installed. those many capabilities can be executed with only one tool: Server Manager. you must have privileges appropriate to the administrative task you want to carry out if Server Manager is to work for you. Server Manager can support Motif−based desktop managers such as XFree86. In particular. PL/SQL.

divides database administration into these categories. Among the significant System Monitors are: • DispatcherMonitors Oracle8i sessions • File I/OMonitors any shared servers • Library CacheMonitors overall I/O 268
. PL/SQL code. spreadsheet application worksheets. a technique that Oracle calls launching in context. and Server Manager commands. Or. among others: • Backing up and recovering a database • Controlling security • Managing a replication environment • Managing instances and sessions • Managing storage • Viewing schema objects Each of these groups offers its own menus and dialogs. or to run Oracle8i scripts on the fly. in a nutshell. Note According to Oracle Corporation. youll see Server Managers Connect dialog box. Administration Manager. Tip You can also jump directly to a specific Server Manager window when you start the Manager. Server Managers most important component and the one youre likely to use most often. a running image of the Oracle8i server. Think of SQL Worksheets as an Oracle8i analog to more traditional.Server Managers copyright window. A context launch can be carried out with a command similar to this:
$ svrmgr connect Server Managers anatomy
Server Managers graphical interface has three major components: Administration Manager. thereby allowing you to edit and rerun commands conveniently. PL/SQL is a full−fledged application programming language that integrates features such as data encapsulation. as well as with a programming environment that extends SQL to enable building applications that include multiple procedures and functions. its first to appear upon startup. PL/SQL combines multiple procedural steps with SQL statements. through which you can connect to an Oracle instance. Oracle8is System Monitors gather and display database performance statistics. and System Monitors. and exception handling with support for distributed computing. but you can also remove the window by one of the following methods: • Pressing any key • Clicking anywhere in the window Next. SQL Worksheets are associated with particular databases and enable you to enter SQL statements. SQL Worksheet. As youve no doubt guessed. that is. disappears in seven seconds.
These worksheets also keep a history of commands you use. structured parameter passing. with the results of those entries automatically being reflected in the active database component.

These items display a window associated with that connection. New Worksheet.
269
. it is associated with the instance and username of your current window. which allows you to choose a System Monitor to start • CloseCloses the current window • ExitExits Server Manager The Administration window.
Connecting to an instance
Tip
You can connect to an Oracle instance by using Server Managers Connect dialog or choosing Connect from Server Managers File menu. allowing you to bring a window to the foreground simply by selecting it in the Window menu. and SYSDBA
Opening new windows
From Server Managers File menu. The Edit menu contains standard editing commands most frequently used when editing text in the SQL Worksheet. you can access the Server Manager online Help system. an SQL Worksheet. or a System Monitor. • MonitorDisplays the Monitor dialog box. The Window menu displays the names of all open Server Manager windows. you can open new windows within Administration Manager. or displays a new Administration window • New WorksheetStarts a new SQL Worksheet. The Connect dialog box allows you to specify: • UsernameOracle username for the database to which you wish to connect • PasswordAppropriate password • Service NameSQL*Net service name for the database to which you wish to connect • Connect AsPop−up menu containing Normal. and Monitor menu items are only available from a window connected to an instance.• LockKeeps system statistics
Server Manager menus
Server Manager offers four main pull−down menus: • File • Edit • Window • Help The File menu items allow you to open or close Server Manager windows and create new connections. When you open a new window. From the Help menu. It offers these selections: • ConnectDisplays the Connect dialog box to connect to an instance and open an Administration window for that database • Administration WindowBrings the associated Administration window forward. SYSOPER.

Using Server Manager in line mode For the Linux traditionalists among us. Scripts are run by using the @ command. end it in either a semicolon ( . but. unlike its handling of multiline Manager commands. For instance. Table 10−8 summarizes the Server Manager commands that are most useful in line mode.
Starting Server Manager in line mode
Server Manager is started in line mode by typing the following at the operating system prompt:
$ svrmgrl
To start Server Manager in line mode and to have it execute a script immediately upon launching.
SVRMGR> @ Name of script file: test
Tip Many Server Manager commands available in line mode can also be used in an SQL Worksheet.SQL. to complete an overall SQL statement. Only valid CONNECT username/password [user] combinations can [password] 270 Meaning Run the command whose name you specify in the parameter script.
Table 10−8: Summary of Server Manager Commands Command @ (at symbol) Use Run scripts containing SQL. and Server Manager commands Connect to a database Requirements Syntax You must have @ command = previously created script the script and stored it as an operating system file. Rather. ) at the end of the statement itself. doesnt require you to end multiline SQL statements in any continuation character. or a forward slash ( / ) on its own last line of the SQL command sequence. PL/SQL. Server Manager also accepts single− or multiple−line SQL statements. Server Manager also offers a command−line interface. On the other hand.
CONNECT
user: Any valid Oracle username for the current database. to run a script called BASEBALL_STATS. Server Manager will prompt for one. whatever its length. youd type this command. Single−line Server Manager commands need no terminators. use a command similar to this:
svrmgrl command=@some_oracle8_script Working with Server Manager in line mode
Heres a precis of working with Server Manager in line mode. password:
.
@baseball_stats
If you dont provide a script name. Server Manager commands may span lines if each such line terminates in a backslash ( \ ) to indicate continuation.

successfully connect.
None
SET [parameters]
CHARWIDTH integer: Sets column display width for CHAR data. SYSOPER: connect as the system operator. disables echoing of commands. LONGWIDTH integer: Sets column display width for LONG data. MAXDATA integer: Sets maximum data size.
271
. OFF. ECHO: ON enables echoing of commands entered from command files. None
[path to image] password corresponding to [SYSOPER] the specified username. path [SYSDBA] to image: A valid specification for an instance/database combination. NUMWIDTH integer: Sets column display width for NUMBER data.ORA
Escape to the OS command line and display the Oracle initialization file. CONNECT scott/tiger AS SYSDBA DISCONNECT Drop the current connection.
EXIT
Quit line mode. INSTANCE instance−path: Changes the default instance for your session to the specified instance path. SYSDBA: connect as the database administrator.
DISCONNECT
EXIT
HOST
SET
Disconnect from an Oracle server Exit Server Manager line mode Execute anoperating system command without exiting linemode Set or change characteristics of the current command−line mode session
You must be connected to a database. LOGSOURCE pathname: Specifies the location from which archive logs are retrieved during recovery. examples: CONNECT.
None
HOST cat INIT. RETRIES integer: Sets number of retry attempts used with the STARTUP command. Users connecting as SYSOPER or SYSDBA must have privileges appropriate to accessing the SYS schema. thedefault. CONNECT scott/tiger.

RETRIES: Number of retries that will be attempted when restarting an instance in parallel mode. DATEWIDTH: Column display width for DATE data. You 272
STOPONERROR ON: If a command file incurs an error. Otherwise. optionally closing and
You must be connected to a database as INTERNAL. or SYSDBA. INSTANCE: The connect string for the default instance. CHARWIDTH: Column display width for CHAR data. SPOOL: If spooling is enabled. displays OFF. AUTORECOVERY: If autorecovery is enabled.
. and SGA (System Global Area).
Shut down a currently running Oracle instance. TERMOUT: If output to the terminal is enabled SHUTDOWN ABORT: Fastest possible shutdown. Does not close or dismount the database. LONGWIDTH: Column display width for LONG data. PARAMETERS: Current values for one or more initialization parameters. displays OFF.SHOW
Show settings currently in effect
None
SHUTDOWN. Otherwise. NUMWIDTH: Column display width for NUMBER data. SYSOPER. terminate. but does shut down the instance. Does not wait for calls to complete or users to disconnect. ECHO: If commands from command files are echoed. SHOW ALL: All settings except for ERRORS. Returns the value LOCAL if SET INSTANCE has not been used. SERVEROUTPUT: Displays ON if output from stored procedures and functions is enabled. displays the name of the output spool file. PARAMETERS. LOGSOURCE: Archive log location. STOPONERROR: If not errors encountered during execution of command files will stop execution of the file. MAXDATA: Maximum data size.

and closes and dismounts the database. Finally. OPEN: Mounts and opens the specified database. MOUNT: Mounts a database but does not open it. PFILE=filename: Causes the specified parameter file to be used while starting up the instance. shuts down the instance. FORCE: Shuts down the current Oracle instance (if it is running) with SHUTDOWN ABORT. before restarting it. SYSOPER.
Start an Oracle instance with any of several options. NORMAL is the default. or SYSDBA. NORMAL: Waits for currently connected users to disconnect. EXCLUSIVE: Specifies that the database can only be mounted and opened by the current instance. Finally.dismounting a cannot be connected database via a multithreaded server
STARTUP. prohibits further connects. PARALLEL: Must be specified if the database is to be mounted by multiple instances concurrently. You cannot be connected via a multithreaded server
Requires instance recovery on next startup. IMMEDIATE: Does not wait for completion of current calls. Does not require instance recovery on next startup. RESTRICT: Only allows Oracle users with the RESTRICTED SESSION system privilege to connect to the database. shuts down the instance. Does not require instance recovery on next startup. Does not wait for connected users to disconnect. prohibits further connects. and closes and dismounts the database. including mounting and opening a database
STARTUP You must be connected to a database as INTERNAL. SHARED: same as PARALLEL
273
. and therefore should normally not be used.

this script runs at system startup and shutdown. of course. and then runs the daemon with those options.
MySQL
This section looks at MySQLs most important administrative features: • Starting the server • Stopping the server • Starting the client • Stopping the client • Creating and deleting databases • Basic security provisions and permissions • Connecting remotely Starting the server You can start the MySQL server. you can add appropriate stop (or start) commands to the shell initialization file /etc/rc.server to use the OS command cd to change to the directory appropriate to your installation before the script runs safe_mysqld. .local. as these examples illustrate:
# mysql. the daemon mysqld.server. But when invoked at the command prompt. 1. Run the script mysql.server start # mysql.server to pass any other needed or nonstandard options to safe_mysqld. it changes directory to the MySQL installation directory. Run the script safe_mysqld. that is.Basic Operations
This section offers a more detailed discussion of common Linux DBMS administrative tasks.server is housed in either the subdirectory share/mysql under the main MySQL directory.server stop
Tip In most implementations the script mysql. You can. the script mysql. also modify mysql. you could append the following:
/bin/sh −c cd /usr/local/mysql . which tries to determine the proper options for the MySQL server daemon mysqld. and then itself invokes safe_mysqld. Most often.server stop
You can also take down mysqld manually with this command:
mysqladmin shutdown
In addition. As a result. Tip In the opinion of many DBMS−saavy folks. in either of two ways. it can take the arguments start or stop. running safe_mysqld is the more reliable option. Stopping the server When used in its most common form. Tip Before the script mysql./bin/safe_mysqld &
274
. Modify mysql. or the subdirectory support−files of the MySQL source file subsystem. you may need to edit the script if youve installed to a nonstandard path. 2.server stops the MySQL server by sending a signal to it with the command:
mysql. For example.server launches mysqld.

log
Examine these garnered lines for any references to path−related problems. if you wish to control the MySQL server globally.sock
port=3456 [mysql.log. use the OS command tail to copy the last few lines of each.server]
user=mysql basedir=/usr/local/mysql
Debugging starting and stopping However you start mysqld.sock as the TCP/IP socket MySQLs protocols will use Defines the port number 3456 as the TCP/IP port MySQLs protocols will use Identifies all lines that follow until the next line encased in square brackets is encountered as pertaining to the script mysql. Such files usually have names of the forms host_name. you can do so by placing a file called my.cnf file.server Identifies the user mysql as the user under whose permissions the script will run Identifies the path /use/local/mysql as the starting point which the script will use in seeking DBMS files and commands when it runs
datadir=/usr/local/mysql/var socket=/tmp/mysqld. Failure of mysqld to start properly usually is related to mysqlds being unable to find the MySQL data directory where it expects that directory to be.cnf Line [mysqld] Effect Identifies all lines that follow until the next line encased in square brackets is encountered as pertaining to the MySQL server daemon mysqld Defines the path /use/local/mysql/var as the location of MySQLs data directory Defines the file whose full path name is /tmp/mysqld.sock port=3456 [mysql.err or host_name. for log files.
275
.
Table 10−9: Understanding my.cnf in the /etc directory as shown here:
[mysqld] datadir=/usr/local/mysql/var socket=/tmp/mysqld. for example:
$ tail doli.err $ tail doli. After youve located these files. look in the data directory. if it fails to launch correctly.server] user=mysql basedir=/usr/local/mysql
Table 10−9 defines each line in this sample my. typically /usr/local/mysql/data for a binary distribution or /usr/local/var for a compiled source distribution.Or. where host_name is the name of your server host.

take these steps. you should then determine what options mysqld expects. 3. or even another instance of the MySQL server. it. Do so with a command like this:
$ mysql trek_trivia
Replace the fictitious database name trek_trivia with the name of the database you wish to access. rerun ps. even if these exist in nonstandard locations. Starting the client: connecting to the server Starting a MySQL client is synonymous with causing that client to connect to its MySQL server. too. Tip Should it be safe_mysqld that fails to start properly. To correct this problem./mysqld −−basedir=/usr/local −−help
The error
Cant start server: Bind on TCP/IP port: Address already in use
indicates that some other program. Run the operating system command ps to determine if another mysqld server is running.What safe_mysqld Wants safe_mysqld normally can start a server that was installed from either a source or a binary version of MySQL. even when invoked from the MySQL installation directory. by invoking the daemon with the −−help option. 1. this time looking for such processes as telnet or ftp. Its a pretty good bet that one of these is using the port or socket mysqld wants. is already using the TCP/IP port or socket mysqld is trying to access.
276
. If no extra copies of mysqld are running. stop it with the OS command
kill PID
replacing the generic parameter PID with the process ID number reported by ps for the superfluous server. Just supply the correct path to mysqld and any other path names it needs to function correctly. and what its default path settings are. you can correct any errors by specifying appropriate pathnames as command−line arguments to mysqld. 2. If such a superfluous server is running.
$ . which assumes youre running it from the directory in which the daemon lives. safe_mysqld must be able to locate them by absolute pathnames. • Should it not find mysqld and its databases relative to its working directory. The sample command below. Then. safe_mysqld expects one of the following conditions to be true: • The server daemon mysqld and the databases it will present must exist in subdirectories of the directory from which safe_mysqld is invoked. Tip Normally you only need to tell mysqld the full path name of the base directory under which MySQL was installed. However.
If it turns out that pathing problems have caused mysqld to fail to start correctly. such as /usr/local/libexec or /usr/local/var. illustrates this process. can be modified.

mysql u root Connect to the MySQL server −w or −−wait and with the privileges of the indicated user. rather than caching them first. name indicated command. that is. −D or −−database=name mysql −−database= Start mysql with the indicated eastern_thought database (eastern_thought in this example) already loaded. executes the trek_good_guys(id INT. Table 10−11 discusses the most important mysql commands. Table 10−10 summarizes MySQLs most useful options. mysql t < some_query > Present output in table format. When used in a batch mode. mysql displays the results of any queries to it as an ASCII table. wait a bit. −e or −−execute=command mysql −e CREATE TABLE Starts mysql. and gives examples of each. mysql −−wait Should the attempt to connect to the MySQL server abort. −H or −−html mysql −−hyml Produces HTML output. When used interactively. mysql presents its results in a tab−separated format. and then VARCHAR(20)) quits. in this example one named some_machine. and then retry connecting. You must distinguish mysql commands from mysql options. −q or −−quick Print results one record at a −t or −−table time. −ppassword or mysql −pabcdef Connect to the MySQL −−password= server with the privileges associated with the indicated password. with each record on a new line. trek_trivia −h or −−host= mysql h=some_machine Connects to the indicated host.mysql is a simple SQL shell that is usable either interactively or in batch fashion. −u or −−user= some_output_file Because such format is the default. Option −B or batch Sample Syntax mysql −−batch
Table 10−11: Important mysql Commands
277
. −C or compress mysql −−compress Use compression in client/server exchanges. this option is only useful when running mysql in batch mode.
Table 10−10: mysql Options Effect Display results separated by tabs. through a script of some kind.

exit mysql exit Terminates the mysql session. Use the mysql commands process list and kill to terminate the client. Creating and deleting databases In MySQL. use syntax similar to this:
# mysqladmin CREATE DATABASE IF NOT EXISTS pittsburgh_pirates
Such a command would create a new. As such.
Command connect
Example mysql connect
Figure 10−1: By the time we supplied the appropriate process ID to the command kill. Or.Effect Reconnects to the active server. or from within a MySQL session. Figure 10−1 below illustrates. had already ended. you can create or delete databases from the operating system command line with the utility mysqladmin. pittsburgh_pirates Tip Any mysql command can be run from either the operating system command line. Stopping the client From the system administrators perspective. status mysql status Displays status information on the MySQL server. 1. the process in question. the client session. then supply that PID to the kill command to terminate the session. with the (optional) database specified by the argument db=. with the initial keyword mysql.
mysql> CREATE DATABASE IF NOT EXISTS pittsburgh_pirates
278
. use mysql use Uses the named database. 2. Use the operating system command ps to obtain the process ID or PID of the MySQL client you wish to kill. you have two methods available for terminating a MySQL client. that is. From within a MySQL session. connect to the MySQL server on the host indicated by the optional argument host=. as illustrated in Table 10−8. use a command similar to this at the mysql prompt to accomplish the same thing. or from within a mysql session. empty database called pittsburgh_pirates if no such database already exists. a MySQL session is nothing more than a user−initiated process running under Linux. at the mysql prompt mysql>. source mysql source some_file_name Executes the SQL script file whose name is given as an argument. From the OS command line.

all available privileges on all WITH GRANT OPTION. GRANT RELOAD.
Table 10−12 elaborates on these commands. that is. you must be logged in as the root user to the same machine on which mysqld runs. The second means of adding or modifying user privilege information is to use the INSERT command directly to modify MySQLs user table. Define a user who can connect to the MySQL server on the local machine. MySQL offers two means of establishing new users and defining their access privileges within MySQL: • Using GRANT statements at the mysql prompt • Manipulating MySQL grant tables directly The following code fragment illustrates using GRANT statements to establish new users and their MySQL privileges:
$ mysql −−user=root mysql> GRANT ALL PRIVILEGES ON *. In addition. on localhost. no matter from where the user someone@% IDENTIFIED BY their_password someone connects.Basic security provisions To use the mysql client to set up new users. that is. that the root user has the insert privilege for the mysql database and also has the more general reload privilege. To 279 Example $ mysql −−user=root mysql mysql> GRANT ALL PRIVILEGES ON *. databases.PROCESS ON *.
Table 10−12: The GRANT Command Effect Connect to MySQL as the root user.* TO admin@localhost.* TO someone@"%" IDENTIFIED BY their_password WITH GRANT OPTIO mysql> GRANT RELOAD. mysql> GRANT ALL PRIVILEGES ON *.
.PROCESS ON *.* TO Give the user someone. Furthermore. give this user the ability to do absolutely nothing. all available privileges on all databases.* TO someone@somewhere IDENTIFIED BY their_password WITH GRANT mysql> GRANT ALL PRIVILEGES ON *. Assign this user the administrative privileges reload and process. However. and then to use the RELOAD command to refresh MySQLs grant tables. but require them to connect to MySQL with a password. Give the user someone. without having to supply a password. you must have ensured.* TO dummy@localhost.* TO Define a user who can connect to the MySQL server admin@localhost. allow them to grant privileges to other users. on localhost. GRANT USAGE ON *.* TO someone@somewhere IDENTIFIED BY their_password WITH GRANT OPTION. on the local machine. Furthermore. or to flush a number of its features such as logs. mysql> GRANT USAGE ON *. this command does not give the defined user any database−related privileges.* TO dummy@localhost. who connects from the host called somewhere. These privileges enable a user to reload or refresh a database. However. without having to supply a password. but require them to connect to MySQL with a password. allow them to grant privileges to other users. the USAGE privilege assigns no privileges. prior to the login in question.

Select_priv. you have problems.somebody.
280
. follow these guidelines whenever possible. Create_priv.trek_rtivia.DELETE. When running MySQL.Update_priv. change. Set a root password.User.Y. and update values in grant tables: xmysqladmin. Do not give your applications any more access privileges than what they need. • Learn the MySQL access privilege system.Drop_priv) VALUES(localhost.Y. If not. Your identity is based on two pieces of informationthe host from which you connect and your MySQL username. the server denies access to you completely.
To modify an existing users privileges using GRANT statements.PASSWORD(captain)). youre ready to carry out tasks such as: • Verifying connections • Verifying requests • Securing connections The MySQL Project has a number of concerns about and recommendations for ensuring the security of remote connections to a MySQL server.User.INSERT.* TO somebody@somehost IDENTIFIED BY captain. use syntax similar to this:
$ mysql −h library −u ref_desk
Having connected.Insert_priv. mysql> INSERT INTO db (Host. • Consider having your application connect to the database using a different username than the one you use for administrative purposes. Never grant privileges to all hosts.Delete_priv.Y).UPDATE.Password) VALUES(localhost. mysql_webadmin. • Try mysql u root. the server accepts or rejects the connection based on your identity and whether or not you can verify your identity by supplying the correct password.Y. Do not grant any more privileges than are necessary. use commands similar to these:
$ mysql −−user=root mysql mysql> INSERT INTO user (Host.Y.
Tip There are three utilities on the MySQL Web site in the Contrib directory that you can also use to insert. Connecting remotely To connect to MySQL on a remote machine.somebody. and xmysql.Db. the server accepts the connection. The GRANT and REVOKE commands are used for restricting access to MySQL. use GRANT statements similar to these:
$ mysql −−user=root mysql mysql> GRANT SELECT. Otherwise. mysql> FLUSH PRIVILEGES.grant an existing user additional or new privileges. • Use the command SHOW GRANTS and check to see who has access to what. mysql> FLUSH PRIVILEGES.Y. and waits for requests.DROP ON trek_trivia.CREATE. Remove those privileges that are not necessary using the REVOKE command. If you are able to connect successfully to the server without being asked for a password.
Verifying connections
When you attempt to connect to a MySQL server.

connecting from any host % Any user. or columns_priv tables. If you run mysqld as another 281
. the server enters stage 2.
Securing remote connections
To make a MySQL system secure. etc. For example. the server determines the users database−specific privileges by checking the db and host tables.
Verifying requests
After you establish a connection.
$ mysql −u root mysql mysql> UPDATE user SET Password=PASSWORD(new_password) WHERE user=root. db. reload. mysqld can be run as any user. if you want to execute mysqladmin shutdown but your user table entry doesnt grant the shutdown privilege to you.
2.gov fred fred. Remember that anyone can log in as any other person. the server checks only the user table entry. access is denied without even checking the db or host tables.155. access is granted. The following example illustrates how several combinations of Host and User values in user table entries apply to incoming connections
thomas. follow these suggestions. (They contain no Shutdown_priv column.loc. connecting from thomas. so there is no need to do so. connecting from thomas.The server accepts the connection only if a user table entry matches your host name and username. connecting from the host with IP address 144. Use passwords for all MySQL users.166. When a connection is attempted. For administrative requests (shutdown. the server looks through the sorted entries and uses the first match found. mysql> FLUSH PRIVILEGES. host.155. because that is the only table that specifies administrative privileges. 1. and you supply the correct password.loc. MySQL will not match host names that start with digits and a dot. For each request that comes in on the connection.loc. update.gov Any user.177
Tip In an effort to preclude hacking attempts based upon this syntax. If the global privileges in the user table are insufficient. tables_priv.). Access is granted if the entry allows the requested operation and denied otherwise.gov thomas. You can also create a new UNIX user mysql to make everything even more secure. the server first checks the users global (superuser) privileges by looking in the user table entry. and so on).gov % fred fred. The grant tables are manipulated with GRANT and REVOKE commands. These privileges can come from any of the user. Dont run the MySQL daemon as the UNIX root user.loc. connecting from any host 144.166. based on the type of operation that you wish to perform.) For database−related requests (insert. This is where the privilege fields in the grant tables come into play. the server checks whether you have sufficient privileges to perform it.177 fred fred. If the entry allows the requested operation.

Table 10−13 summarizes what we consider the most important such options. This could be abused.
−−skip−grant−tables
−−skip−name−resolve −−skip−networking
PostgreSQL
This section details PostgreSQLs most important administrative features: • Starting and stopping the server • Starting and stopping the client • Creating and deleting databases • Basic security provisions and permissions • Connecting remotely
282
.UNIX user. 3. Dont allow TCP/IP connections over the network. all files generated with SELECT INTO OUTFILE are readable by everyone. Finally. The file privilege may also be used to read any file accessible to the UNIX user that the server runs as. This gives everyone full access to all databases! (You can tell a running server to start using the grant tables again by executing mysqladmin flush−privileges or mysqladmin reload. 5.) Host names are not resolved. you can launch mysqld with command line options that affect security. Consider creating a user named mysql for that purpose. Dont give the file privilege to all users.
Table 10−13: mysqld Security−Related Options Option −−secure Effect IP numbers returned by the gethostbyname() system call are checked to make sure that they resolve back to the original host name. because the MIT−pthreads package doesnt support UNIX sockets. The output of mysqladmin process list shows the text of the currently executing queries. because MySQL usernames have nothing to do with UNIX usernames. This makes it harder for someone on the outside to get access by pretending to be another host. for example. Any user that has this privilege can write a file anywhere in the file system with the privileges of the mysqld daemon! To make this a bit safer. 7. You can edit the mysql. 6. Causes the server not to use the privilege system at all. All connections to mysqld must be made via UNIX sockets. which can then be read with SELECT. so that a MySQL root user can log in and check things even if all normal connections are in use. so any user who is allowed to execute that command could see whether another user issues an UPDATE user SET password=PASSWORD(not_secure) query.server script to start mysqld as another UNIX user. On UNIX platforms. This option is unsuitable for systems that use MIT−pthreads. mysqld reserves an extra connection for users who have the process privilege. you dont need to change the root username in the user table. This option also adds some sanity checks of host names. and you cant overwrite existing files. 4. All Host column values in the grant tables must be IP numbers or localhost. Normally this is done with the su command. by using LOAD DATA to load /etc/passwd into a table. do not run mysqld as root unless you really need to. Dont give the process privilege to all users. Check that the UNIX user that mysqld runs as is the only user with read/write privileges in the database directories.

it must be started as a background process. you can run more than one postmaster if each occupies its own directory and uses a distinct port number. manages conversations between client and server. Generic syntax to start postmaster with its most useful features looks similar to this:
postmaster [ −D data directory ] [ −N maximum number of servers ] [ −i ] [ −p port number ]
Heres a rundown of this syntax and its effects. only one postmaster should be running within a file subsystem at any given time. furthermore. can be used to kickstart software that should be up and running as soon as a Linux machine boots.
Startup Scripts Startup scripts.
Multiuser server
postmaster.pid # # Source function library. but not before it can release system resources such as shared memory.Starting and stopping the server PostgreSQL enables you to launch or stop both multi− and single−user servers. but can be set as high as 1024 • −IPermits TCP/IP connections • −p portIdentifies the TCP/IP port or local socket file extension on which the postmaster should listen These sample commands start a multiuser postmaster:
% nohup postmaster >logfile #Starts postmaster on the default port. use a command similar to this:
% kill 15 process ID of the server you want to kill
Such syntax will stop postmaster.3−2 Lamar Owen # description: Starts and stops the PostgreSQL backend daemon that handles all database request # processname: postmaster # pidfile: /var/run/postmaster. However. • −D data directoryIdentifies the root of the set of database directories • −N maximum number of serversSets the maximum number of server processes that the postmaster may start. and allocates memory and other system resources. And. sending system messages #regarding the launch to a file in the active directory called #logfile % nohup postmaster −p 1234 & #Starts postmaster on the indicated port
To stop a multiuser server. One example of using such a file to start the PostgreSQL postmaster might be:
# #! /bin/sh # postgresql This is the init script for starting up the PostgreSQL server # Version 6. default is 32. postmaster does not itself interact with the user. the PostgreSQL multiuser backend to the database server.
283
. commonly known as rc files.5.

this option passes dates to and from the client in European or dd−mm−yyyy format • −o OutputFileSends all debugging and error output to the indicated file • −sPlaces statistics. defaults to the value of the USER environment variable Caution While the postgres backend most frequently runs directly from the shell rather than in background. • −D data directorySpecifies the root of the set of database directories • −EEchoes all queries • −S sorting memory sizeSpecifies the amount of memory available to sorting and hashing operations before disk caches will be drawn upon • −eIf supplied.
pg_ctl
PostgreSQL offers another utility. each servicing an individual PostgreSQL server. restart) $0 stop $0 start . including time of run.. dont run it in this way. pg_ctl.... at the end of each query • database nameSpecifies the name of the database to be served out by postgres. Generic syntax for the most useful postgres single−user server features looks similar to this:
postgres [ −D data directory ] [ −E ] [−S sorting memory size ] [ −e ] [ −o output file ] [ −s
Lets look more closely at this lineup. A single−user server need not be run in the background and offers different arguments than its multiuser peer. stop) echo −n "Stopping postgresql service: " killproc postmaster sleep 2 rm −f /var/run/postmaster. stop. with which you can start. status) status postmaster . restart. or find the status of a postmaster. Its generic syntax comes in four flavors:
pg_ctl [−w] [−D datadir][−p path] [−o "options"] start
285
. access the same set of databases intended for the postgres backend youre working with.pid rm −f /var/lock/subsys/postgresql echo . *) echo "Usage: postgresql {start|stop|status|restart}" exit 1 esac exit 0
Single−user server
The command postgres starts a single−user database server.fi . that is in foreground. if multiple postmasters.

necessitating database recovery at next startup. • > pg_ctl startA no−frills startup • > pg_ctl −w startStarts postmaster but blocks any requests to it until it has been confirmed to be running • > pg_ctl −p /usr/local/pgsq/bin/postmaster startStarts postmaster with the full path of its binaries specified • > pg_ctl −o "−p 5433" startStarts postmaster on a specific port The following are some examples of stopping a postmaster with pg_ctl: • > pg_ctl stopNo−frills stop • > pg_ctl m smart stopStops postmaster after waiting for all clients to log out The following examples use pg_ctl to restart a postmaster: • > pg_ctl restartNo−frills restart • > pg_ctl −w restartRestarts postmaster after blocking any requests to it until postmaster is confirmed to have shut down and to have restarted. Specifies the path to the postmaster executable image. fast or ffast mode: rolls back active transactions. a postmasters status may be reported as sleeping.
Table 10−14: Understanding pg_ctl Effect Waits for the database server to come up.. output is of the form: pg_ctl: postmaster is running (pid: 1234567) In addition to running. start Starts postmaster. and precludes abrupt and possibly problematic disconnecting of clients that are still engaged in completing a transaction." appropriately enough. Some examples of pg_ctls use follow. All assume the default PostgreSQL prompt. Finally. The "w" stands for "wait. to use pg_ctl to get some basic information about a postmasters status. Specifies database location.pg_ctl [−w] [−D datadir] [−m [s[mart]|f[ast]|i[mmediate]]] stop pg_ctl [−w] [−D datadir] [−m [s[mart]|f[ast]|i[mmediate]] [−o "options"] restart pg_ctl [−D datadir] status
Table 10−14 elaborates on these syntax elements. restart Restarts postmaster. status Shows postmasters current status. immediate or iimmediate mode: aborts backend processes. Specifies options to be passed directly to postmaster. use the following command:
> pg_ctl status
Element −w −D datadir −p path −o options
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. Options usually are embedded in single or double quotes to ensure that they are passed to postmaster as a group. times out after 60 seconds. −m mode Specifies the shutdown mode: smart or ssmart mode: wait for all clients to log out. stop Shuts down postmaster. that is carries out a complete stop/start cycle.

a user may type queries or commands. psql. 287
. the PostgreSQL interactive terminal. you supply the name of the database to which you wish to connect. Its generic syntax looks like this:
psql [ options ] [ database name [ user name ] ]
As this syntax indicates. or off if this format is already in use. which as shown above includes the name of the active database. • \HToggle HTML output format for queries on. Type: \copyright for distribution terms \h for help with SQL commands \? for help on internal slash commands \g or terminate with semicolon to execute query \q to quit
blues_db=>
At the prompt. For example. Some of the most useful psql commands include: • \connect (or \c) [ database name [ user name ] ]Connect to a new database under the indicated user name. the command
$ psql blues_db
Tip
results in a display similar to this:
Welcome to psql. which might induce errors. psql assumes that argument is a database or username.Such a command might produce output similar to this:
pg_ctl: postmaster is running (pid: 13718) options are: /usr/local/src/pgsql/current/bin/postmaster −p 5433 −D /usr/local/src/pgsql/current/data −b /usr/local/src/pgsql/current/bin/postgres −N 32
Starting and stopping the client A single command. first closing the existing connection. You can use these options to make the connect more efficient: • hostname of the PostgreSQL server to which you wish to connect • port number on the PostgreSQL server through which you wish to connect • username under which you wish to connect psql accepts these parameters under the respective options: • −d: database • −h: host • −p: port • −U: user Be careful in supplying these psql options and their arguments. initiates or terminates PostgreSQL client sessions. Should an argument be presented to psql that it cannot understand.

on those flavors of Linux that use the bash shell. that is. postgres will only connect under the account that will own the server process. Creating and deleting databases PostgreSQL offers a number of commands that pertain to creating and deleting databases. this section explores them. You cannot run the database server as root. • \l or \listLists all databases and their owners that are on the server.• \i fileTakes as input from the indicated file commands to be executed. A sample of initlocation looks similar to this:
initlocation /usr/local/src/pgsql/current/data2
Caution To use initlocation. before users or access controls have been created. you must be logged in as the database superuser. but at the same time. you: • Create the directories in which the database data will live. Caution Never run initdb as root. a new collection of postgres databases that are all: • Administered by the same user • Distributed by a single postmaster Generic syntax for initdb that reflects its most significant options is:
initdb [ −−pgdata=data directory or −D data directory ] [ −−pwprompt or −W ] [ −−pglib=director
Lets examine these parameters more closely.
initlocation
The command initlocation establishes a secondary PostgreSQL storage area. you can also create a secondary database storage area at least partially from the operating 288
. Whats more. • \qQuits psql.
initdb
initdb creates a new PostgreSQL database installation. Therefore. • Create the template1 database. • −−pgdata=data directory or −D data directorySpecifies where in the file system the database should be stored • −−pwprompt or WCauses initdb to prompt for the password of the database superuser • −−pglib=directory name or −l directory nameTells initdb where to find initialization files To create a database system. and thereby block access to those files for other users. template1 houses tables that supply such facets as built−in data−type definitions. tables that dont belong to any particular database. • Generate shared catalog tables. serves as the blueprint for all new PostgreSQL databases that you create thereafter. that is. Tip On some platforms. initlocation takes only one argument: a directory or full path name. that is. running initdb as root might assign ownership of needed files to root. a near−doppelganger for the Bourne shell. as its name suggests. that server needs to access files initdb creates. which. during initialization.

However. it only stands to reason that you must be either the database superuser or the owner of the database to be deleted to run dropdb.
289
.system. the command dropdb deletes an existing postgres database. which runs under the postmaster on host pets. you could use absolute paths:
$ initlocation /opt/postgres/data dropdb
As its name suggests.
youll know that dropdb failed. in turn. youll know that the database you told it to delete was indeed removed. which. which listens at port 5678. results in a display similar to this:
Database "cats" will be permanently deleted. if you see this message :
dropdb: Database removal failed.
dropdb is actually a shell script wrapper around the SQL command DROP DATABASE. Tip Because dropdb destroys an existing database. runs under psql. as the following example shows. The generic syntax of its most useful elements is:
dropdb [ −h host name or −− host host name] [ −p port number or −−port port number] [ −U user n
These parameters have these effects: • −h or hostHost name of the machine on which the postmaster controlling the database to be deleted is running • −p or portTCP/IP port or local socket file extension on which the postmaster controlling the database to be deleted listens • −U or usernameUser name under which you wish to connect in order to delete a database • −W or passwordForce a prompt for the database superuser password • −i or interactiveIssues a verification prompt before doing anything destructive • dbnameName of the database to be removed If you see the message
DROP DATABASE
after running dropdb. As a result: • dropdb must be able to find psql • A database server must be active on the host dropdb and psql target • All default settings and environment variables used by psql or the PostgreSQL client library libpq will apply to dropdb Here are a few examples of using dropdb: • $ dropdb eastern_thoughtDeletes the database eastern_thought on the default PostgreSQL server • $ dropdb −p 5678 −h pets i catsDeletes the database cats.
$ export PGDATA2=/opt/postgres/data $ initlocation PGDATA2
Note Alternatively.

results in this display:
CREATE USER "wheeley" NOCREATEDB NOCREATEUSER
290
. and bypasses prompts concerning wheeleys capability to create databases or other users by supplying the −D and −A options. which listens to port 5678.Are you sure? (y/n) y DROP DATABASE "cats" DROP DATABASE
Basic security PostgreSQL is nothing if not straightforward in its naming of its most important user management toolscreateuser. Only users with the account characteristic usesuper enabled. only users who can temporarily take on superuser privileges. you will be prompted for a username if you fail to specify it from the command line when running createuser Now lets look at some examples of using createuser. • $ createuser tomCreates a new user tom on the default database server. createuser is actually a shell script wrapper that can be run under psql for the SQL command CREATE USER. which must be unique among all postgres users.
createuser
createuser creates a new postgres user. produces the following display:
Is the new user allowed to create databases? (y/n) n Shall the new user be allowed to create more new users? (y/n) n CREATE USER
• $ createuser −p 5678 −h nirvana −D −A wheeleyCreates the user wheeley using the postmaster on the host nirvana. that is. executed as DROP USER. and dropuser. executed as CREATE USER. Therefore. can create new postgres users. createuser requires that • It must be able to find psql • A database server must be running on a targeted host • Any default settings and environment variables available to psql and the libpq front−end library be applied to createuser createusers general syntax is quite simple:
createuser [ options ] [ user name ]
createusers most important options are: • −h host name or −−host host nameHost name of the machine on which you wish to create a user • −p port number or −−port port numberTCP/IP port or local UNIX domain socket file extension on which the postmaster for the database in which you wish to create a user listens • −d or −−createdbCreates a new user who can create databases • −D or −−no−createdbCreates a new user who cannot create databases • −a or −−adduserCreates a new user who can create other users • −A or −−no−adduserCreates a new user who cannot create other users • −P or −−pwpromptCauses createuser to issue a prompt for the password of user being created • usernameName of the postgres user being created.

As a result.As youve probably deduced. Only users with usesuper set can destroy postgres users. Had it encountered any problems. youd instead have seen something similar to this. but only after prompting for and receiving confirmation
$ dropuser −p 3456 −h federation −i elmo User "elmo" and any owned databases will be permanently deleted.
createuser: creation of user "username" failed dropuser
dropuser removes an existing postgres user and the databases owned by that user. which name must exist in the postgres installation. Like its counterpart that expedites adding users. you will be prompted for a name if none is specified on the command line The next two examples illustrate how dropuser is used: • To remove user leo from the default database server
$ dropuser leo
• To remove user elmo using the postmaster listening at port 3456 on the host called federation. dropuser is a shell script wrapper around the SQL command DROP USER that runs from psql. the message
CREATE USER
indicates that createuser ran successfully. Are you sure? (y/n) y DROP USER "elmo" DROP USER
As the last example above indicates. dropuser must: • Be able to find psql • Be able to connect to a database server at any indicated host • Apply to itself any default settings and environment variables available to psql and the libpq front−end library dropusers syntax mirrors that of createuser:
dropuser [ options ] [ username ]
These are the parameters usable with dropuser: • −h host name or −−host host nameName of the machine on which postmaster runs through which dropuser will work • −p port number or −−port port numberTCP/IP port or local UNIX domain socket file extension on which the postmaster listens for connections • −i or −−interactivePrompts for confirmation before actually removing a user • usernameName of the postgres user to be removed. the response
DROP USER
291
.

However. Its format is:
host db 123. one of the suites several supported security mechanisms.45.67. verification of the users actual identity can take place in either of two ways. more extensive sample above also defines a home directory and default shell for the user in question. encrypted password Such records might look similar to this:
some_one:/wnsargset6435 somebody_else:/ v398476h#e+wq::/home/somebody_else:/bin/tcsh
Tip The second.255. it does more than change the PostgreSQL password of the indicated user.conf. It also causes the previous version of the DBMS password file to be renamed to passwd.255. Thus.250 255.255.bk.67.255.255. the PostgreSQL password file consists of records made up of two fields.45. Given these supporting files and formats. Entries in the password file must adhere to the conventions used for identity authentication in the PostgreSQL configuration file pg_hba.250 and the subnet address 255. running pg_passwd looks similar to this:
% pg_passwd passwd Username: some_one Password: Re−enter password:
When pg_passwd runs in this way. • The first field contains a username • The second field holds the accompanying. any subnet • The fifth field indicates that a password will be required • The final field specifies that any of the passwords found in the PostgreSQL password file will be accepted The PostgreSQL password file uses the same format as the operating system password files /etc/passwd and /etc/shadow.255 password passwd
In such a line: • The first field represents the host to which a user may be authenticated • The second field represents the database to be accessed • The third and fourth fields indicate that a user may connect from the IP address 123. and that elmo had not been deleted as a PostgreSQL user.
pg_passwd
The utility pg_passwd manipulates some of PostgreSQLs password file functionality.
User authentication
In PostgreSQL. authentication means that the server and postmaster ensure that the user requesting access to data is in fact who the user claims to be. The message
dropuser: deletion of user "elmo" failed
would have told you something had gone wrong.tells you that dropuser executed successfully. All users who invoke postgres must be cleared to do so. that is. 292
.

usesuper set. drop table. If the passwords match.conf file which specifies what authentication method will be used. and destruction of system catalogs (or modification of their schemas) is never allowed.0 crypt Access control
Postgres provides mechanisms to enable users to limit the access that other users can have to their data.255 trust # This machine cannot be trusted in any way.255.0. the retained. only operate for the owner of the class. which is transmitted to the server encrypted.255.10 255. host all 127. where it is compared to the users password as it appears in pg_shadow. effective user ID serves is used as the basis for subsequent access control checks. such operations are never permitted on system catalogs. silently bypass all access controls.0 255.0. The following example illustrates some of the effects of these authentication methods on the PostgreSQL password file. and at the server it is compared to that users password as it appears in the pg_shadow table. 2.168. which is used to match the supplied password rather than the pg_shadow table. using the operating system call crypt(3).usecatupd set. usually handled by grant or revoke • Class removal and schema modificationCommands that destroy or modify the structure of an existing class. which is. that is.0. From the network: When PostgreSQL is distributed. • passwordThe user must supply a password. ID. These definitions.0.
# Trust any connection via Unix domain sockets. local trust # Trust any connection via TCP/IP from this machine. transmitted to the server in the clear.255.0 password # These machines must send encrypted passwords. No other authentication takes place.0. • cryptThe user must supply a password. rely on the nature of the host attempting the connection and the database that host is attempting to access.1 255.3 255.255. Tip Database superusers. and changes the identity of the user attempting to connect to PostgreSQL to that of the user postgres. Available categories of access include: • Access privilegeUsed to limit reading. host all 192. the connection is allowed.0 reject # This machine cant encrypt. 293
. users who have the environment variable pg_user. however. and drop index.
Authentication types
PostgreSQL supports several authentication methods for both UNIX and TCP/IP domain sockets: • trustThe connection is allowed unconditionally. • rejectThe connection is rejected unconditionally. in turn. such implementations must include a configuration file pg_hba.255. as opposed to OS login. An optional password file may be specified after the password keyword. writing and setting of rules on classes. From the user shell: A backend server started from a user shell notes the users effective. so passwords will be sent in clear. such as alter. host all 192. host all 192. with two exceptions: manual system catalog updates are not permitted if the user does not have pg_user. As a result.168.255.255. However. In addition. any of its users by definition have access to the TCP/IP port at which the postmaster listens. the connection is allowed. If the passwords match.168.255.1.

some encryption is better than none at all. If the two values are equal. needs almost no effort. That is. Connections made via the Internet or using TCP/IP within an Intranet rest on pg_liba. that is.conf records of the following format. made part of a Boolean expression that translates as both this and this must be true. Most Linux distributions now understand encrypted passwords. starting and stopping an Oracle8i server. to control who can connect to where from where. More to the point for us: • PostgreSQL supports a number of variants of the MD5 encryption algorithm in addition to crypt(3). very fast encryption method) ♦ SSL • MySQL supports both crypt(3) and SSH
Oracle8i
This section examines the most important administrative features of Oracle8i: • Starting the server • Stopping the server • Starting the client • Stopping the client • Creating and deleting databases • Basic security • Connecting remotely Starting and stopping the server Whether youre operating in a graphical or command−line environment.conf will be used. and then compared to the TCP/IP address and mask of the client attempting to connect. PostgreSQL handles remote connections by what it calls host−based access control.
294
.Connecting remotely As it does with connections to local postmasters. remote connections rely on the configuration file pg_hba. • Oracle8i supports these encryption algorithms: ♦ DES (standards−based encryption) ♦ DES40 (for international encryption) ♦ RSA RC4 (a very secure. an instance or running copy of the server executable.
When Some Encryption Is Better Than None While crypt(3) is a weak encryption algorithm. that is. the remainder of the record in question comes into play. in the PGDATA directory of the PostgreSQL implementation.
host database TCP/IP address TCP/IP mask authentication method
The TCP/IP address that appears in such a record is logically anded. defining the method by which the attempt will be authenticated. Should a connection address/mask combination match more than one record.conf. the first such matching record in pg_liba. to the specified TCP/IP mask.

1. it involves the CONNECT and DISCONNECT commands. Any Oracle8i database launches by using a parameter file. datafiles.
Starting and stopping in Server Manager line mode
To start an Oracle8i instance in the command−line Server Manager mode. Server Manager prompts for them. Starting and stopping the client As is the case with all the DBMSs Ive discussed. 3. As part of creating a new database. simply enter the STARTUP command and any appropriate options at the Server Manager prompt. for example:
svrmgr> STARTUP
Refer to Table 10−8 for details on the parameters available to STARTUP. Server Manager brings up the Connect dialog box. if you omit the username parameter. if you omit either or both of the parameters username and password. 2. Open an SQL Worksheet. inspect and edit at least the following parameters of the new parameter file. To create a parameter file for a new database.Starting and stopping in Server Manager GUI mode
To start an Oracle8i instance in the graphical Server Manager mode. Make complete backups of all existing databases before creating a new database. use the Linux command cp to make a copy of the parameter file that Oracle8i provided on the distribution media. Tip In line mode. Enter a command such as:
STARTUP
• or
STARTUP RESTRICT
• or
STARTUP PFILE=some_file
Refer to Table 10−8 for details on the parameters available to STARTUP. Backup should include parameter files. Consult Table 10−8 for syntax and parameters for each. redo log files. Whether thats done from the graphical or line modes of Server Manager.
Creating and deleting databases Oracle Corporation recommends the following sequence of steps for creating and deleting a database in Server Manager GUI mode: 1. and control files. take these steps. which should contain the parameters 295
. Each database on your system should have at least one customized parameter file that corresponds only to that database. Tip In an SQL Worksheet. 2. starting and stopping a client under Oracle8i is synonymous with a client connecting to or disconnecting from a server.

8.
The items and information in the example statement above produce a database with the following characteristics: • Names the file mukachevo 296
. An Oracle8i instance identifier must match the value of DB_NAME to preclude confusion with other instances during concurrent operations.
Creating and deleting in line mode
Command syntax similar to that outlined in Table 10−8 is all thats needed to create a database in Oracle8i Server Manager line mode. 5. 4. Tip When an instance starts before a database has been created.DB_NAME DB_DOMAIN CONTROL_FILES DB_BLOCK_SIZE. 7. and so on. check the instance identifier of the one youre creating. choose the Startup Nomount radio button. If you have other databases. use the SQL command CREATE DATABASE. name the files and set their sizes. establish maximum numbers of files. In this dialog. DB_BLOCK_BUFFERS PROCESSES ROLLBACK_SEGMENTS LICENSE_MAX_SESSIONS LICENSE_SESSION_WARNING LICENSE_MAX_USERS
supplied with values appropriate to your hardware. Oracle performs the following operations: ♦ Creates datafiles ♦ Creates control files ♦ Creates redo log files ♦ Creates SYSTEM tablespace and SYSTEM rollback segment ♦ Creates data dictionary ♦ Creates users SYS and SYSTEM ♦ Specifies the character set in which data will be stored ♦ Mounts and opens the database for use Caution Make sure that the datafiles and redo log files that you specify do not conflict with files of another database. the instance starts. optionally setting parameters within the statement to name the database. connect to the server as an administrator. mukachevo_log2b) SIZE 500K. and DBMS implementations. GROUP 2 (mukachevo_log2a. When you execute a CREATE DATABASE command. Start an instance to be used with the database youre creating by using Server Managers Startup Database dialog box. DATAFILE mukachevo_system SIZE 10M. Make a full backup of the new database to ensure that you have a complete set of files from which to recover it. To create the new database. Upon selecting this button. operating system. mukachevo_log1b) SIZE 500K. only a System Global Area and background processes exist for that instance. The following example illustrates this process:
CREATE DATABASE mukachevo LOGFILE GROUP 1 (mukachevo_log1a. 6. Start Server Manager.

Larger cache size reduces the number of disk writes needed to record modified data. Examples are:
LICENSE_MAX_SESSIONS = 50 LICENSE_MAX_USERS = 30
Tip
297
. Tip Oracle Corporation strongly recommends at least two control files. which is a rough approximation of the minimum number of buffers the cache should have. for every database you create. should that block size be increased. Typically. set PROCESSES to at least 40. as in University of Pittsburgh. Tip Thrashing. • DB_BLOCK_BUFFERSNumber of buffers in the buffer cache in the System Global Area. Make sure that the filenames listed to CONTROL_FILES match no existing filenames. each of them stored on a separate physical drive. a large cache may take up too much memory and might induce memory paging or swapping.• Assigns a SYSTEM tablespace to one 10MB datafile named mukachevo_system • Receives two online redo log groups. or even thrashing. • DB_BLOCK_SIZEDefault data block size for any Oracle8i server depends on operating system block size. but with a small operating system block size. the value of DB_NAME is recorded in the datafiles. redo log files. DB_NAME must be a string of no more than eight characters. a value for DB_NAME might be
enrollment. Place each control file on separate physical disk drives by fully specifying filenames that refer to different disk drives for each filename. and control file of the database. Only when dealing with a system with a lot of memory and speedy drives.pitt
• CONTROL_FILESInclude the CONTROL_FILES parameter. Estimate the number of data blocks that your application uses most regularly. include table. though. if you anticipate 35 concurrent users. Follow these guidelines for such files: List at least two filenames for the CONTROL_FILES parameter. During database creation. one of the more descriptive data processing terms. unless you want Oracle to reuse or overwrite those files. index. On the downside. So. and rollback processing in this estimate. • ROLLBACK_ SEGMENTSA list of the rollback segments an instance acquires at database startup Rollback segments refers to a systems swapping data in and out of memory so frantically and frequently that the system slows or even hangs. but usually equals either 2K or 4K. which together form a database name that is unique within a network. DB_DOMAIN typically equals the name of the organization that owns the database. Later attempts to start an instance of or with this database must match DB_NAME. Must include 5 for background processes and 1 for each user process. refers to a systems swapping data in and out of memory so frantically and frequently that the system slows or even hangs. each containing two 500KB members Parameters that can be supplied to CREATE DATABASE include: • DB_NAME and DB_DOMAINLocal name component and logical location within a network structure respectively. So. set its value to a list of control filenames to use for the new database. between 1000 and 2000 buffers suffice. • PROCESSESThe maximum number of operating system processes that can connect to Oracle simultaneously. • LICENSE_MAX_ SESSIONS and LICENSE_MAX_USERSSet a limit on the number of concurrent sessions and concurrent users respectively that can connect to a database.

read but nothing else by members of the owners user group. And the latter is a good thing. or configuration files. • Give all DBA utilities.
298
. wisely. executable. the permission 711. add a Linux user group that consists of users permitted limited access to Oracle8i utilities.Basic security Oracle8i. the permission 700 so that no one other than the DBA user. Publicly executable programs such as SQL*Plus should be executable by this group. Give ownership of these files. or run by their owner. Finally. before installing the server. databases can be accessed solely through the Linux technique of shadow passwords. often called the superuser. the files containing dba−executable programs can be read from written to. into two sets: those executable by any user on the system. Again. The only member of the OS root group should be the superuser. the oracle software owner should not be a member of the group to which the operating system user root. and are completely invisible in every way to all other users on the system. and of the bin subdirectory in which they live. in my opinion. even knows that these files exist. Such ownership helps to ensure that less knowledgeable users cannot. create a database administrators group (dba) and assign the root and oracle software owner IDs to this group. and those executable by DBAs only. so that every operating system user can at least access the Oracle server. Overall. or otherwise alter the nature of Oracle8i data. such as sqlplus. do such things as change access permissions for. because Server Manager system−privileged commands are assigned automatically to the dba group when the Oracle8i server is installed. so that those users can be controlled by the OS files /etc/passwd and /etc/group.
File ownership
The security of an Oracle8i database profits from ownership of all files involved by a user at the Database Administrator or DBA level of permissions. relies largely on Linux to provide database security. 2. too.
Security for utilities
Oracle Corporation makes these suggestions for protecting Oracle8i utilities. • Give all user utilities. and assign group ownership of those utilities to this oracle group ID. That is. Before installing the Oracle server. Oracle Corporation recommends these specific steps: 1. and so that Oracle executables can be divided. group accounts.
Groups and users
To create Oracle8i users and user groups from Linux. That is to say. and the capability of a program to change its user ID upon execution. usually the same as the oracle software owner. rename or move. as they were intended to be. Caution Even though both the oracle software owner and root user should belong to the dba group. set permissions on such files to 710. Furthermore. or what Linux calls the user type other. Programs executable by dba only have permission 710. belongs. inadvertently or otherwise. Oracle8i also imposes special authorizations on the database executable. such as Server Manager. it makes full use of such OS features as file ownership. to the oracle software owner. • Keep all executables in the bin subdirectory of the main Oracle directory.

the oracle software owner should also own directories containing database files. and invisible to all other users. you should see a display similar to this. appear as theyre shown. the −rwsr−s−−x. Use this command to set the UID bit for these files:
$ chmod 6751 $ORACLE_HOME/bin/oracle
• Then use the Linux command ls. Set permissions on these files to 600.Security for database files
Oracle Corporation makes these recommendations for securing Oracle8i database files. that is. • Similarly. Set permissions on these directories to 600 as well. This gives other users temporary access to the files by temporarily giving those users some of the permissions of the file owner. starting and stopping clients. the importance of other Oracle administrative tasks such as starting and stopping the server. and managing security becomes paramount.
Summary
Installing and configuring any Linux DBMS requires you to be comfortable with: • Navigating the server console • Starting and stopping the server • Starting and stopping the client • Creating and deleting databases • Providing basic security
299
. youve been successful in this task:
−rwsr−s−−x 1 oracle dba 443578 Nov 19 13:09 oracle
Connecting remotely Users can access any Oracle8i database across an intranet or the Internet if: • An Oracle8i password file exists • Remote users have an identity defined in that file as well as in the operating system passwd and shadow files • The remote user either connects to the database with the parameter INTERNAL or launches an Oracle application that uses the database Given this ability of users to connect remotely. ensuring that the files will be readable and writeable only by their owner. • To allow users other than the oracle software owner to access database files and directories protected in this way. turn on the set user ID or setuid bit of these files. As long as the first ten column positions of this output. • The oracle software owner should also own all database files.

from Mutiny Bay Software at www. Caution
Open source tools: MySQL
MySQL is even more command−line oriented than PostgreSQL. which are outlined in Table 11−1. when we downloaded kpsql.html.4+ or higher • Qt 1. kpsql.
Table 11−1: Selected MySQL Tools Tool Use Sample Syntax
300
.com/kpsql. is specific to PostgreSQL.1+ or higher • PostgreSQL 6.
Open source tools: PostgreSQL
Although many of PostgreSQLs administrative tools operate in command−line mode. kpsqls features include: • Bookmarks • Color syntax highlighting for its internal editor • Drag−and−drop functionality • KDE desktop integration • Online Help for PostgreSQL and general SQL questions • Query results displayed in HTML tables • Search and replace capabilities in its internal editor • The capability to execute multiple SQL statements • The capability to redirect query output to a file • The capability to cancel running queries kpsql requires: • KDE 1.44+ Be aware that downloads from the Mutiny Bay Web site arent always tidy. MySQL offers several significant tools. For example. Such GUI−based features can help even the most command−line−challenged. and provides a tool similar to Oracles Server Manager Worksheets.
Vendor−Supplied Tools
This section reviews tools supplied by PostgreSQL and MySQL. Windows−wedded DB administrator comfortably monitor his or her PostgreSQL implementation.Chapter 11: Linux Database Tools
This chapter discusses administrative tools available to the Linux DBMSs this book examines. This section summarizes a graphical tool for managing PostgreSQL databases: kpsql. we saw the binary stream that is the executable on our PCs monitor as the transfer progressed. a few exist that provide a GUI interface to administrators.mutinybaysoftware. The third−party product.

−−extend−check: Does a very extensive check of the specified table. the latter specified by a number. or repairs MySQL tables. −−analyze: Analyze the distribution of keys. −e. optimizes. −u. via FTP or other 301
. used to optimize seeks and make table scanning by key faster. −l. local or remote. writes output only upon errors. −−description: Displays basic information about the specified table. −−no−symlinks: Causes MySQL to forego following symbolic links when repairing a table. −s. −−unpack: Unpack a table that was packed with myisampack. that repairs numerous database problems. −i. −−wait: Wait if a table is locked.
−f. −−sort−index: Sorts the index in high−low order. −w. −d. −−force: Overwrites existing temporary files. −−silent: Silent mode. Such files then can be transferred to other users. −−information: Displays statistics for the specified table. $ make_binary_release
make_binary_release
Creates a binary release of a compiled MySQL. checks. −S. −−recover: Recovery mode. −o. −r. −−sort−records=index_num: Sorts records according to an index.
$ myisamchk [options] table_name Significant options: −a. but in a few cases. more reliable. −−safe−recover: Recovery mode that uses a slower. repair method.myisamchk
Describes. −R index_num. You can determine index numbers with the command SHOW INDEX.

MySQLs documentation suggests this two−step process for using msql2mysql. in the bin directory under your MySQL installation directory. close and then immediately reopen logfiles. 1. −−add−locks: Use LOCK TABLES before and UNLOCK TABLE after each table dump. −−all−databases: Dump all databases. −A. 2. create db_name: Create a new database of the specified name. a bug report (or a report about any problem). reloading the grant tables. scripts or SQL files from mSQL. Shell script that converts mSQL programs.
mysqlbug
mysqldump
302
. flush−hosts: Flush all cached hosts. or. mysqlbug can be found in the scripts directory in the source distribution.msql2mysql
such mechanisms. if possible. processlist: Display list of active threads in server. drop db_name: Delete the specified database and all its tables. flush−logs: Flush all logs. This requires the replace program. Run the utility on the msql source. We encourage Script to be used to file bug reports with the MySQL mailing everyone to use the mysqlbug script to generate list. that is. flush−privileges: Flush all grant tables. flushing tables to disk. Recompile. flush−tables: Flush all tables. the precursor of MySQL. Handle most but not all such files. The MySQL Group states. which is distributed with MySQL. and Significant commands: reopening log files. $ mysqladmin command [command−option] command
mysqladmin
Carries out administrative tasks such as creating or dropping databases. for a binary distribution. refresh: Flush all tables. Dumps a MySQL database into $ mysqldump [options] database [tables] an output file which can consist of either SQL statements or Significant options: tab−separated text. to MySQL. shutdown: Stop the MySQL server.

needed if you want to see stats on the components of MySQL databases
303
. All name arguments are regarded as database names.−C. tables. a dump of the schema only. Changes strings in place in files or on standard input. replace Utility used by msql2mysql. Particularly significant to any DBMS administrator are:
mysqlshow
• myisamchk. since it is central to day−to−day administrative tasks • mysqlimport. since it allows the manager to bring text files into MySQL tables easily • mysqlshow. but $ replace a b b a −− file1 file2 which also has more general applicability. −−delayed: Insert rows with the INSERT DELAYED command. −−flush−logs: Flush log files on the MySQL server before starting the dump. −−lock−tables: Lock all tables before starting the dump. −B. −q. −−host=: Dump from the MySQL server on the named host. −−no−data: Write no record information for a table. −−compress: Compress all information between the client and the server if both support compression. −l. −d. columns and indices. In effect. −h. that is. since it contributes to table integrity • mysqladmin. −e. −−extended−insert: Use multiline INSERT syntax for more compact and faster inserts. −−quick: A quick dump. −F. −−force: Dump even if SQL errors occur during a table dump.
Displays information about MySQL databases. $ mysqlimport [options] database_name (to be imported to) text_iunput_file (to be imported from) $ mysqlshow [options] [database [table [column]]]
mysqlimport
Imports text files into MySQL tables. unbuffered and sent directly to standard output. −f. Used to modify strings. −−databases: Dump several databases.

SQL or SQR? No. Windows−based emulation of SQR Server.Report SQR Server: A report−processing and data−manipulation tool that provides native access to more than 60 combinations of databases and operating environments. Weve chosen those tools we feel might be of greatest use to database administrators. Personal SQR allows you to test applications locally on non−Linux clients before implementing them on a back−end SQR Server. the Toolchest gives you template programs that illustrate how each such 304
. Brio Technology means Structured Query Reporting.Report Viewer: A report−viewing utility for Windows clients that displays screen previews of reports prior to printing. • Brio. includes components such as the following. and close.
Brio. Whats more. billed on the Brio Technology Web site as an industrial−strength enterprise−reporting suite. including file operations such as create. open. be run from Windows clients. you didnt just misread that acronym. commercial licenses • Source available: No Brio.brio. from both commercial and open source suppliers.Report Personal SQR: A single−user. and access to multidimensional databases.com • Distribution method: Professional sales. • Brio.
C/Database Toolchest
The C/Database Toolchest in effect allows the addition of DBMS capabilities to existing. The libraries provided with the Toolchest offer more than 150 database management functions. • Author: Brio Technology (some components acquired from SQRIBE Technologies) • Web site: www.Report Builder: A Windows−based graphical development tool that allows you to create enterprise and business−to−business reports. modify. and exception notification. • Brio. and record operations such as add.Insight: A Web browser plug−in that provides optional Web−based interactive analysis and report−viewing capabilities for data delivered within reports produced by means of the Brio SQR Server.Report
Brio. and large at that. SQR Server also enables you to add procedural language and control to SQL queries and commands. a component of a larger suite called Brio ONE. which function in heterogeneous environments that include Linux DBMSs.Report. with one exception. provides DBMS reporting and management tools that can.Third−Party Tools
This section summarizes a number of third−party tools for Linux databases. By SQR. collections of data. • Brio. It includes a graphical query builder that supports multiple queries and nested subqueries as well as report features such as load lookups.Report. find. The latest version of SQR Server has been enhanced to support features such as XML input and output. report headers and footers. and delete. • Brio.

• Author: The CoSORT Company • Web site: www. It can input from or output to new or existing files. and data types. EBCDIC. which can perform tasks such as: • Cross−table matching (joins) • Field selection and extraction • Field−level data−type translations • Mathematical and expression evaluations • Multikey comparisons • Record grouping and filtering CoSORT also includes: 305
. a database manager that accomplishes interactive creation and editing of databases. standards−based. summarization.
CoSORT
CoSORT. and application programs.com/ • Distribution method: Retail • Source available: Yes The Toolchest includes both C and C++ libraries and a simple interface. currency. CoSORT supports many file sizes. CoSORT helps speed up database loads with a minimal time−sorting algorithm employed by a software architecture that transfers records directly through memory and that can make use of direct Sequential Multiprocessing (SMP). for one−pass extraction.mixsoftware. floating point. standard input and to standard output pipes and applications. tape or optical devices. zoned decimal. including alphanumeric and binary forms. and delete • Viewing and compressing databases Finally. • Author: Mix Software • Web site: www. and reporting. these enable you to use the libraries database management functions to support such tasks as: • Converting to and from dBASE data files • File operations like create. commercial−grade sort package for UNIX systems. the first independently−developed. platform−independent database sorting utility. C and COBOL numerics. parallel CPU. and. that is.com/external/products/products. the C/Database Toolchest offers LDM. for providing sort functionality within databases.html • Distribution method: FTP • Source available: N/A CoSORT is a collection of utilities for file sorting. capabilities if they exist on CoSORTs platform. sorting. Together. data warehouses. among them a mainframe−based sort control language called sortcl. open. find.iri. modify.function operates. and most widely licensed. bills itself as the worlds fastest. close • Indexing • Locking • Record operations such as add. CoSORT includes several standalone end−user utilities. and Julian and multinational timestamps. record formats.

The package also offers: • A Spreadsheet Grabber that enables data to be pulled from within a spreadsheet • An ASCII Data Dictionary builder • An ODBC query builder
OpenAccess ODBC and OLE DB SDK
These development kits act as middleware. Inc. and Interactive UNIX. • Author: Conceptual Software. the package provides record filters. • Web site: www. that is. such as: • Desktop applications • Networked enterprise applications • Web servers • XML servers The newest releases of these developers kits include: • Enhanced error checking and error reporting 306
. memory. providing standardized APIs that in turn can be used to create ODBC−compliant drivers and OLE−compatible. Inc. Solaris. and time data types among its most useful features.com • Distribution method: FTP • Source available: No Note OpenAccess is free for individual use (commercial pricing is available on request). for a number of data sources. • Author: Automation Technology. • Web site: www. DBMS/COPY considers its capability to transfer data that involves dissimilar numeric. and computational tools. and disks as CoSORT calls on them • Command−line conversion tools that build UNIX and NT sortcl scripts from mainframe sort control files • Full hardcopy and searchable electronic documentation.
DBMS/COPY for UNIX/Linux
DBMS/COPY is a tool that allows administrators to transfer data between DBMSs and databases with dissimilar record structures. The tool accomplishes this by directly reading and writing databases native binary files.• Automatic and manual resource tuning tools that can be used to fine−tune CPU. variable subsetting. date. online man pages and scripting samples.com/ • Distribution method: N/A • Source available: N/A DBMS/COPY directly reads and writes the native binary files of over 80 DBMSs.conceptual. OpenAccess provides tools to make a data source accessible by means of standard SQL from a number of environments. COBOL. with example calls presented in C. plug−and−play−based access tools. In addition.odbcsdk. and FORTRAN CoSORT supports most flavors of Linux.

middleware designed for e−business. UDBC. such as the command−line utilities offered with MySQL • Tools presented by third parties. including full SQL support.Report and CoSORT Within either category. • Author: OpenLink Software • Web site: www.com/ • Distribution method: FTP and retail • Source available: Yes Note OpenLink Virtuoso is free for individual use (commercial pricing is available on request). OpenLink Virtuoso is a virtual database engine that enables you to view.openlinksw.0 Distributed Queries
OpenLink Virtuoso
Virtuoso. update.0. acts to simplify the creating of XML data from existing HTML files. Among the databases Virtuoso supports are: • DB2 • Informix • Oracle • SQL 92−compliant DBMSs • Sybase
Summary
Management tools that accompany or coexist with Linux DBMSs occupy two categories: • Tools provided by vendors. or OLE−DB connection. JDBC. or manipulate the data stored in dissimilar databases from a single ODBC.
307
. for local and client/server configurations • Support for SQL Server 7. such as Brio. a variety of functions can be found.• Optimized memory management and client/server protocol • Support for multithreading by all components of the OpenAccess SDK • Support for native OLE DB 2. and from SQL−compliant databases.

However. 309
. like designing a database. we speak as if you are building every aspect of the application on your own. However. writing an application was a relatively straightforward task. Subsequent chapters describe in detail how to code an application. Our discussion begins with a description of the architecture of an application that works with a database. all will become clear as we progress into this chapter. this is not the case: libraries and tools will help you with many of the tasks that we describe below. translates the input into SQL calls. Users should think only about doing their job: entering data correctly or extracting the data that is needed. we discuss how to program applications that work with your database. The user should not know or care which data elements are stored in what tables or columns. this was a large. a database application enables users to perform sophisticated tasks on a complex database with a minimum of fussand without harming themselves. is in theory a simple task: it accepts input from a user. the better able you will be to decide whether a given tool can do that job. and doesnt permit the user to fill it with nonsenseis not easy. some of the ideas that we present may strike you as novel or difficult. doesnt trash the database. Every person who used the application logged into the machine that held both the database and the application. Fortunately. The application was a monolithic program that contained all of the code needed to perform all of the applications tasksfrom drawing data−entry screens to interacting with the databases engine. because the better you understand the task that a tool or library must execute. If you are not familiar with networking or object−oriented programming. and the better you will know how to use it. In either case. or you. multiuser machine that ran some flavor of UNIX. In brief. In this and the next few chapters. the application insulates the database from the user. and how to install and administer several popular database packages.Chapter 12: Application Architecture
Overview
To this point.
Evolution of the database application
Building a database application.
What Is a Database Application?
A database application is a program that is used to manipulate data contained in a database. we have discussed what a database is. then passes those SQL calls to the database engine for execution. doesnt break down. or how much storage is available. as you read this chapter. By the way. If you are familiar with object−oriented programming or with networking. you may gain the impression that you must design and build every aspect of the database application on your own. building a robust applicationone that has no holes or cracks in it. what data types are used. Likewise. In most cases. much of the material in this chapter will be familiar to youalthough you may be unfamiliar with some of the details of working with databases. Fifteen years ago. because of the wealth of details to which you must pay attention. the database. but it also stops the user from doing what the user should not do. The application lets the user do what the user needs to do. The application insulates the user from the details of the database. applies domain logic to the input.

Many people were amazed to discover that the worldwide computer network they dreamed of building. but this power had a price: the writing and administration of database applications suddenly became much more complex. Companies wanted tools that would permit users to download data−entry templates and enter information directly into databases. and then the Java language and Java applets. Bodies of data could be made accessible to the public at large. This idea grew slowly. The intranet brought great power. The computer world woke up one day not only to discover that it had a worldwide network. four major shocks have occurred to upset this way of working. Building a mini−Internet within ones enterprise had great appeal: the tools already existed. but that that network had an excellent protocol to which local networks could also adhere. then discovered that the government had already built the interstate highway system. machines and users at widely scattered sites began to exchange data. to exchange data. database servers could begin to talk with each other. flexible. mainly because each manufacturer advocated its own proprietary networking protocol. The Internet The next shock was the Internet. but the seeds were planted that grew into todays networked environment. its existence became widely known only in the late 1980s. Its as if Henry Ford designed the Model T. Suddenly. however. the Web turned the Internet from a preserve of hackers and academics into a commercial bonanza. By inviting the public to come and view a companys wares. Intranets The final shock was the idea of applying the Internets protocols to internal networksto intranets. users were familiar with the Internets standards.Since then. a user could log into the machine from a remote site. These led to the creation of HTML forms and CGI interpreters. dont worrywe explain them in this chapter. Overnight. and proved to workand that were in the public domain. (If some of these terms are not clear to you. the ability to break a database application into modules that could be relocated over a wide−area network became a necessary part of any database package. Furthermore. Developers began to work with the idea that an application could be two programsone that ran on a personal computer and the other that ran on a server machineand so the idea of client−server architecture was born. The Web Then came the World Wide Web.
310
. Although the Internet has been around since the 1960s. already existed. and the intranet could be plugged into the Internet itself with a minimum of trouble. the public discovered that the federal government had created a set of networking protocols that were robust. The Web brought two powerful enhancements to the Internet: graphics and the idea that bodies of data could link themselves to each other through universal resource locations (URLs). Furthermore. as they are called. Networks The first shock was the advent of networks. albeit crudely.) Suddenly.

In the following section.
Bottom tier: Access to the database
This tier is the data sourcethat is. or give a team a negative number of runs. plus drivers and networking software with which your application accesses the engine. and performs a well−defined task upon it. These almost always come from third−party providers. So what. Fortunately. we defined step 5 of designing a database as the task of writing domain−integrity rules. Thus. and integrity refers to the soundness of the data being entered. of course. engineers have created a model to help us manage the building and administration of a database application: the three−tier model. For example.Costs and benefits
As you can see. or an acknowledgment that the statements were processed. In the phrase domain integrity. and executes them. since the early 1990s. the word domain refers to a domain of knowledge. is business logic? You may remember that. A domain−integrity rule can be prescriptive as well as prohibitive. The tiers of the three−tier model are described in the following sections. and presenting data appear almost weekly. It then receives the engines reply to those SQL statementsdata. New ways of organizing.
The Three−Tier Model
The three−tier model divides a database application into three sections. but a well−designed database application will avoid such blurring as much as possible. when we discussed database design in Chapter 4. It is fair to say that the world of database applications is still trying to cope with these changes. there will be some blurring of the tasks that each tier performs. We also place in the bottom tier the code with which your application converses with the data source. or an error statementand returns that reply to the tier above it. This tier receives instructions from the tier above it. or tiers. In theory. If all goes well. It comprises the database engine. baseball or librarianship. In practice. in our baseball database. These changes bring great power to users and programmers. you may be asking. Each tier receives data. the software that controls access to the data themselves. a domain−integrity rule would ensure that a user could not enter a tie score. to a cluster of programs that are scattered across a network. we explore the three−tier model and discuss a few of the many ways in which it can be implemented on a computer network. distributing. it returns an error to the data source. and that can be made accessible to users around the globe. for example. no tier duplicates the work performed by any other tier. the database application has evolved from a monolithic program that runs on one machine. the tier then forwards the data. a domain−integrity rule is a rule that helps to ensure that the data being entered are sound with regard to the area of knowledge with which the database is concerned.
Middle tier: Business logic
The middle tier contains business logic. if an error occurs. but they also multiply the details that an applications programmer must manage. For example. if you are writing a database 311
.

Some experimental databases are experimenting with incorporating business logic directly into the database. neither should have any knowledge of what is in your database. This tier accepts instructions from the tier above it. It then displays what the middle tier returns to iteither data or an error message. The top and bottom tiers should be contextlessthat is. No tier should have any knowledge of the other tiers. or how your database is structured. are called the database applications domain logic or business logicusually the latter. accepts what the user types or clicks. However. when taken together. it should contain all of the logic with which your data 312
. the domain−integrity rules are not part of a relational database per se.for a hospitals heart−transplant program. Likewise. if a person tries to borrow a book that was previously borrowed and whose return was not recorded. execute them. and return the results to the middle tier. a domain−integrity rule may force your application to modify the database on its own in order to keep the database synchronized with reality. As we noted in Chapter 4. and then lets the current user borrow it. It then receives in reply something from the tier below it. The top tier should simply receive input from the user. and compares the domain−integrity rules that are programmed into it. thus. process it. The presentation logic encompasses all of the many details of the interface. the bottom tier should receive instructions from the middle tier. The term presentation logic is used to describe the design that underlies the user interface. such as: • How the interface is broken into screens • How the screens flow into each other • How fields are arranged within each screen • How error messages and information messages are presented • The rules for which graphical widget to use. they must be implemented separately. The middle tier then forwards data to the bottom tier for interaction with the database. and forwards it to the middle tier for processing.
Top tier: User interface
The top tier holds the user interface. the database application marks the book as having been returned. this is particularly true of the object−relational databases. in our library example in Chapter 4. and it forwards to the top tier what the bottom tier returns in replydata or an acknowledgment that the instructions were processedand forwards it to the tier above it. Rather. and forward it to the middle tier. Rather. one domain−integrity rule will tell the database to mark the donor patient as having died the day his heart is transplanted into another patient. if any • How color is used • How icons and graphics are used
How the tiers relate to each other
Each tier performs a task that is both well defined and discrete. and returns that something to the tier above it. The middle tier is where the applications business logic is implemented. and forwards the modified data to the tier below it. all a tier should know is that it receives data from the tier above it. Or. No tier should duplicate work performed by any other tier. The middle tier should be the only tier that knows about the content and structure of your database. the typical commercial relational database currently does not have this capacity. Thus. as part of the application. It displays data and instructions on the users screen. The set of domain−integrity rules. does something to those data.

which is named mysql. If the design is sound. • The top tier is the script itself. Its easier for a human being to think clearly about a complex task by dealing with it one piece at a time. It also enhances the reusability of our code. and the password from the mysql interpreter. 313
. the engine is a daemon named mysqld. lets look more closely at what actually would occur were we to invoke the MySQL interpreter to interpret one of our examples: • When we invoke the interpreter. So. its first task is to establish contact with the SQL engine. we presented some simple database applications: our example SQL scripts. we can use it repeatedly to perform the same task in other applications. then it passes that call to the engine. how do these entities relate to the three−tier model? • The bottom tier is comprised of the mysqld server. we can distribute those programs over a network. At first glance. and the database engine. • If the daemon mysqld discovers an error in any statement.are processed. problems are easier to isolate and fix. because we can place one piece of our application onto one machine and funnel the input from several other machines into it. or even broken into more than two separately running programs. • The interpreter mysql then begins to read and execute the SQL instructions from our script.
Three−tier model: An example
In Chapter 3. we make each module easier to design.
Benefits of the three−tier model
The three−tier model for database applications offers several significant benefits: • Easier designBy organizing an application into tiers. each of which performs one well−defined task. and debugged separately. Under MySQL. It translates each raw SQL statement into a call in MySQLs call−level interface (CGI). just as the pieces of a jigsaw puzzle fit together to form a picture. The software that comprises the bottom tier almost always are programs that run on their own machine. After we have built and debugged a module to perform a task reliably. which turns SQL statements into CLI calls to the database engine. The server checks the login and password. and confirms that the user has permission to connect to the database. which then prints an error message. This lets the labor of managing an application be shared among the machines in the network. we discuss in detail how the pieces of the three−tier model can be organized. then all of the debugged pieces should fit together to form the full application. • Easier implementationEach piece can be written separately. the login. • mysqld receives the name of the database. So. However. the interpreter. • ReusabilityDatabase applications perform the same tasks repeatedly. it notifies the interpreter. Later. even the interpretation of simplest of all database applicationsa SQL scriptinvolves communication among three separate software entities: the script. We must emphasize that the tiers of the three−tier model are logical. the interpreter closes contact with the engine and exits. a script is too simple to fit into the three−tier model. Because each piece performs one well−defined task. or broken into two programs. • When the script has concluded. to execute. • DistributabilityWhen an application is a set of programs that talk with each other. which executes our SQL instructions. the top and middle tiers may be lumped into one large program. and the mysql interpreter.

In this context. these terms are also used to describe machines. As you can see. or two tiers may be broken into one program and the third tier into another. the client usually is a PC that is running a flavor of Windows and is being used by a human being. and server programs can be run on server machinesbut not always. whereas the server is a machine that is running UNIX or Windows NT. You probably are familiar with clients and servers. This section presents a few of the commoner ways in which the tiers of the three−tier model are implemented. or one program may contain the top tier and part of the middle tier. • A server is a program that receives a request for a service from a client.
Organization of the Tiers
The three−tier model is a template with which we organize our work. Client programs are usually run on client machines. programs One problem with the terminology client and server is that the terms are used ambiguously. A server may also be a client. So. we must do all our domain−level checking by hand. and executes it. when you run the X Window System on your Linux. but in case you are not. However. • In general. and it requests services from the bottom tier. As described here. as part of its work. it means a set of programs that interact with each other. When we work directly with SQL. However. even if not present physically as a body of code. and a second program contain the rest of the middle tier. • The middle tier can be both a client and a server: it fields requests from the top tier.• And the business logic of the middle tier? It resides in our heads. all three tiers may be bundled into one program. without the assistance of software. that is. • The bottom tier is almost always a server: it fields requests from the middle tier. the three tiers are present even in an extremely simple applicationlogically present. Both client and server programs can be run on a single machine. if your Linux box is plugged into a network that includes other boxes that run X programs. you are running both client programs and a server program on the same box. An application can implement its tiers in many ways. a server can service multiple clients simultaneously. how does this relate to the three−tier model? As follows: • The top tier is always a client. the following defines them briefly: • A client is a program that issues a request for a service. it may issue a request for service from another server. Our point is that the tiers are conceptual rather than physical. and that provides services via a network to a cluster of client machines. Thinking about your application as being formed of three tiershowever those tiers are coded into programswill help you to design a program that is both easier to build and easier to maintain. then you can invoke clients from those other boxes and run them on your console through your machines X server. Machines vs. the programs often are organized into clients and servers. Although we organize a database application into three tiers.
314
.
Clients and servers
When tiers are implemented as separate programs. it does not follow that a database consists of three separately running programs: rather. for example.

We discuss this issue in more detail later in this section. However. it is the tier that is most likely to change frequently. your users are running that fat client on their PCs and accessing the database over a network. If. and put the top tier into a skinny client. each tier can be implemented either as separate programs. when we discuss programming the user interface. we say so specifically. the better. or you may run any permutation of this architecture. and shows how their drivers fit into the architecture of a database application. you must give an altered copy of the application to every person who uses it. or they can be bundled together into one large program. As a rule of thumb. we refer to programs that can be distributed across one or more machines. Physically. Every time you alter your database or the logic of a tier. when the client program contains only the top tier. then you must somehow put a copy of that fat client into each users hands every time you modify it. The following introduces each of these APIs. this is an administration issue. Because the middle tier is the only one that knows about your database. When we mean machines rather than programs. For the most part. So why. As you can imagine. which. it can matter a great dealbut not because of any issue that is intrinsic to designing a database application. then the skinnier you can make the client. with the other tiers run as one or more server programs. or you may run the top tier alone on your box. then you will have to replace only the one copy of the server program to make most alterations available to every user of your application. This is a set of calls that are implemented in one or more languages (often C). then a fat client works quite well. rather than the machines themselves. ODBC As we noted in Chapter 3. If all three tiers are implemented as separate programs. 315
. that pass SQL statements directly to your database packages engine. however.
Drivers
In our discussion of the three−tier model. Contrariwise. SQL instructions are passed to a SQL engine through a call−level interface (CLI). Fat versus thin clients The tiers of the three−tier model are logical entities. replacing these fat clients can be quite a problem. When all users log into your machine and use one executable program to access your database. it often is called a fat client. in turn. so long as the three tiers are implemented somehow? Actually. The most commonly used drivers are built around Microsofts Open Database Connectivity (ODBC) application−program interface (API) and Suns Java Database Connectivity (JDBC) API. requests services from a bottom tier located on a third machine. Thus. you may run all three tiers on your local box. when we speak of clients and servers. if you can implement the middle tier within a server program. then the client sometimes is called a thin or skinny client. if your users are running over a network.And so it is with the tiers of a database application. and request service from a middle−tier server that is located elsewhere on your network. you ask. When a client program has more than one tier built into it. Rather. it is becoming common to have a driver stand between the database engine and the application. should it matter how the tiers are bundled. we speak of the bottom tier as accessing the databases engine directly.

In the client− oriented architecture. The server−oriented architecture differs from the client−oriented architecture in three key aspects: • The client machine does not need the database vendors proprietary networking software to communicate with the engine. but it does not define the syntax for the CLI. Under this architecture a user must purchase an ODBC driver manager for each of the users PCs. the driver receives these calls. The server makes the translation from ODBC to the database−specific CLI. The driver manager is linked directly into the application. the ODBC driver manager on the clients Windows machine loads the Informix ODBC driver. each relational database package has its own CLI. the user must purchase a copy of the appropriate ODBC driver and a copy of the database vendors proprietary networking software. The result is the ODBC API. needs its own ODBC driver. Furthermore. 316
. the ANSI/ISO standard for SQL defines a syntax for SQL itself. as we noted in Chapter 3. and yet another for Oracle release 7. Standard networking software is sufficient. and no two are compatible. As you can imagine. However. the other is server oriented. In this architecture. in turn. this situation is a serious obstacle to porting a database application from one relational database package to another. and then forwards those database−specific calls to the databases engine. • The client machine needs only one general ODBC driver. Thus. The application issues calls in the ODBC CLI. and each major release of each package. rather. the ODBC driver (or drivers) reside on the users computerusually a PC that is running some version of Microsoft Windows.
ODBC client−oriented architecture
In the client−oriented architecture. For example.So far. However. a different driver is needed for Informix release 6. Each ODBC driver uses the database vendors proprietary networking software to connect to the database engine. and forwards them to the copy of I−NET (Informixs networking tool) that resides on the clients machine. consider an application that is working with Informix. ODBC is a major step toward opening up database connectivity. loads at runtime the drivers that it needs. One architecture is client oriented. this architecture uses an ODBC driver manager to ensure that a given ODBC call is directed to the correct driver. and thus to correct database. implementations of ODBC use two architectures that are mutually incompatible. an ODBC driver is needed for Informix release 5.
ODBC server−oriented architecture
Some companies support ODBC systems that use a server−oriented architecture. in turn. it simply communicates with the ODBC server. a group of software companies led by Microsoft Corporation formed a consortium to design a common CLI for all relational databases. The ODBC driver translates the ODBC calls into Informix ESQL calls. an ODBC driver stands between the database and the application. This driver does not translate ODBC. Thus. To alleviate this situation. not by the driver. translates them into the CLI expected by the target database package. Because an application may work simultaneously with two or more brands of database. I−NET. so good. It also complicates writing a multitier application that works with more than one brand of relational database package. the ODBC driver on the client machine communicates with an ODBC server on the server machine. For example. for each brand of database with which each PC works. The following explains these two architectures. talks across to the Informix engine that resides on the server machine. as it was meant to do. In ODBC. each database package. the driver manager.

all we have to do is replace that one copy. the JDBC−to−ODBC architecture is more general purpose. In this model. One way to do this is to use the CGI. in theory. in that one JDBC driver will. Like ODBC. works by passing calls to a JDBC driver. talk with all ODBC drivers or servers. A company that implements the server−oriented architecture still must make a major investment in software. The strategy of using one centrally located copy of a program is relatively easy to do for the middle and bottom tiers of a database application: they can be implemented as centrally located servers. easy to use. the top tierthe tier with which the user interactsmust run on the users machine. JDBC uses two different architectures to talk with the database engine: In one architecture. thus. when users are scattered across a network. The JDBC driver translates JDBC instructions into the CLI recognized by the brand of database to which the JDBC driver is talking. however.
From Tiers to Programs
The Web has become the gold standard for providing users with access over a network to a body of information. when we modify the database or fix a bug. in effect.• The server machine needs no more than one ODBC driver for each brand of database that it supports. Such a system is considerably easier to set up and manage than is one that uses the client−oriented architecture. JDBC is. to record information collected from users and to take orders for goods. and through a servlet. but less than what is required by the client−oriented architecture. the JDBC driver talks to an ODBC driver or server. The 317
. and centrally stored. and it depends upon the ODBC driver or server to manage the task of talking with the database engine. the Java counterpart to ODBC. The JDBC driver translates its JDBC instructions into ODBC calls. and the modification or bug fix is immediately available to all users. the JDBC driver talks directly to the database engine. This is not a problem if all users log into the machine on which the database is stored. Providing access to a database over the Web has become an extremely important aspect of the Web. through an applet. Ideally. and is downloaded to a users machine every time a user requests the forms URL. The JDBC−to−engine architecture is specific to a given brand of relational database. putting a copy of the updated program into users hands can be a problem. In the other architecture. with that copy located on a machine that we control. yet available to many users over Internet. like ODBC. we want to reduce as much as possible the number of copies of any program that comprises a database application. however. JDBC The JDBC API is a set of objects that are written in the Java programming language. The graphical capabilities of the Web format give companies a way to build front−end clients that are complex. we would have only one copy of every program. However.
Common Gateway Interface
As you may recall from our earlier discussion of fat versus thin clients. an HTML form that gathers data from a user is stored on a central server machine. The rest of this section introduces the three major ways with which a Web page can interact with a database: through a common gateway interface (CGI) program. The JDBC API.

a CGI program can become impossibly difficult once it involves more than a fairly small number of forms. the program is responsible for processing the data.data that the user writes into the form is then downloaded to a program that is located on your central machine. Thus. the browser and the server may be passed a large number of data back and forth. this approach raises problems with regard to the different ways that browsers implement scripting languages. you can embed within a Web page an applet that performs a complex taskan animation. An applet gives a programmer access to the entire range of graphical and communications functionality that are built into the browsers engine. CGI has two serious limitations: • CGI severely restricts what you can do on the clients machine. The browser invokes another program. checking what a user has input for consistency and correctness is best performed on the client side. and the CGI program must parse and interpret a large number of parameters. Thus. However. say. other applet systems are also in use. it receives a form from the user. However. and is downloaded by the same server that downloaded the page. Java is the most popular language for writing applets. However. A CGI program can be supplemented with a script written in JavaScript or a similar scripting language. writes output to the browser. interacting with the database. with that copy used by everyone across the network. then dies. but they can have limitations that are addressed by the other methods of working over the Web: applets and servlets. therefore. The only restriction is that this server must reside on the same machine as the HTTP server with which you downloaded the applet. and constructing the HTML that is returned to the user. to execute the applet. all it knows are the data that the browser sends to it. or a complex interaction with the user. that is. you can build low−level error checking into the applet. An applet is requested from within an HTML document. Thus. an applet has access to the full range of graphical objects that reside in the engine. and have that one copy used by every user on your network. CGI programs are quite useful: they are simple to write and maintain. if the execution of a task requires a user to work with a number of forms. As you can see. • The middle−tier server can be programmed to remember the applets state. to pass onto the client tasks that are best performed on the client side but that cannot be executed in HTML. Thus. CGI programs can be quite useful. this lets you program complex graphic tasks.
Applets
An applet is a program that is downloaded to a Web browser. Flash 318
. an applet gives you a way to build a top−tier program that is centrally stored yet is available to all users on the network. applets remove the limitations that are built into CGI: • An applet can use a socket to plug itself into a middle−tier server. and then incorporates the output it receives from that program into the page that it displays to the user. such as dragging objects. However. rather than submitting what the user enters to the server and having the server discover the error. for example. CGI lets you have one copy of a top−tier program. Furthermore. you can store one copy of an applet. Some tasks are best performed by the client rather than by the server. • Finally. The applet can interact with the server on a field−by−field basis. and they can perform a wide range of tasks. because it is written in a fully featured language. Thus. Like a CGI script. processes it. the browser interprets it. It does not remember what the user has done from one form to the next. or engine. one applet can be run under every operating system and microprocessor upon which the browser has been implemented. And although the applet performs complex tasks. rather than in batch mode. • A CGI program is stateless.

Rather. • A top tier. a servlet is not uploaded to the client machine. however. In this case. The program on the users machine is the client. Cross−Reference We introduce PHP and give an example of coding servlets in Chapter 13. Unlike an applet. we introduced the three−tier model for database applications. However. The clientin this case. To begin. you do not have to worry about having to run your code on a variety of client machines. In practice. a user who is working with a Web browser asks an HTTP server on a given server for an HTML page. When the user begins to work with the applet. because it requests services. such an applet could well be very large and take a long time to download. of database applications. in particular. in turn. With a servlet. the program on the users machine that holds the top tiersends requests for services to the centrally located program that holds the middle and bottom tiers. many of which you do not have available for testing. or structure. and prove that it works before you put it into production. or as individual programs that communicate with each other. Servlets have one major disadvantage: they consume resources on the machine that is running your Web server. which interacts with the database.applets. This architecture is of almost Byzantine complexity. they have a huge advantage: because they are run on a single machine that you control. This model views an application as being comprised of three tiers: • A bottom tier.
Servlet
A servlet resembles an applet: it is a small. you can write your code. has a request for an applet built into it. It may well be that a program that contains the top tier is run on the users machine. A network introduces another level of complexity to the organization of tiers into programs. or any combination thereof. PHP is a popular language for writing servlets. this page. • A middle tier. the tiers are said to use a client/server architecture. which contains all business logicthat is. The tiers can be organized in a number of different ways: either lumped into one large program. the applet begins to exchange information with the database via JDBC driver. the servlet is managed by the HTTP server with which the users browser is working. the Web server invokes the servlet and passes data between the browser and the servlet. the logic that manages domain−level integrity and that manages the passage of data into and out of the database. and that the top tier communicates with a program that resides on a central machine and that contains the middle and bottom tiers of the application. The JDBC driver either works through an existing ODBC driver or communicates directly with the database. One major advantage offered by Java is that its JDBC API lets an applet interact directly with a database on a remote server.
Summary
This chapter introduces the architecture. which interacts with the user. the better. and to make the applet a fat client. however. When a user requests a service of the servlet. It is possible to build the middle tier into an applet. because it executes requests for services from one or 319
. test it. For example. discrete program that holds business logic. the more functionality that can be off−loaded onto a middle−tier server. the program on the centrally located machine is the server. but in practice it works quite smoothly. are becoming quite popular.

Using drivers makes it easier to write an application that can work with more than one brand of relational database package. As a rule of thumb. and servlets. A thin or skinny client is one that contains only the top tierthat is. so as to reduce the number of copies of a given program that are in circulation. a skinny client is preferable to a fat client. there are exceptions to this rule. Two of the more common are drivers that use the ODBC protocol. Finally. it only contains the user interface. The three most common methods by which a database can interact with the Web are through the CGI. If more than one tier is included within the client program. However. However. giving the Web access to a database is becoming more and more important. it may also use one or more drivers that stand between the engine and the applications bottom tier.
320
. it is said to be a fat client. or the JDBC protocol. Java applets. In many instances. the bottom tier will communicate directly with the database engine.more clients.

and an example of a language−library interface using PHP. Much of this is expected and. To support these productivity−enhancing tools. It is common to have a preferred API for use with databases and even operating systems. An example of a language−library interface is PHP and its available drivers. a different driver for ODBC (C/C++).
321
. entirely. it turns out. One final word of warning. let alone that every database vendor implements the same API the same way. End−user access is another matter. and so on. there needs to be a specific MySQL driver for DBI (Perl). and so is sometimes the preferred choice. then the remaining option is a call−level interface (CLI) offered as a library for a specific language. the database can be switched to any other having the same API without impacting the database application. It bears repeating. So. This chapter discusses the main industry−standard database APIs. however frustrating and time−consuming it may seem. For each standard database API there needs to be specific database drivers that act as the functional layer that translates the more generic API and the particular way each database implements the API. Read the vendor−supplied documentation very carefully. We say client tool because database server products are actually distinct computer programs that operate quite independently of the tools and utilities that interact with them. that if all else fails the command−line tools and utilities are capable of performing everything that can be done. We make use of PHP with MySQL in the chapter on Web−enabled database applications. Call−level interfaces expose more of the internal operations of the database servers. For the Microsoft Windows product line. The advantage of using a standard database API is that. in theory. not yours) for client access is ODBC using C/C++ or possibly Visual Basic as the programming language. the under−the−hood stuff. very efficient for database administrators (DBA) and technical support staff for these databases. the API of choice (theirs. The following is a quick rundown of some common combinations of language and industry−standard database APIs: • DBI with Perl • ODBC with C/C++ • JDBC with Java If an industry−standard API is not available. an example of how to use the command−line client tool that ships with MySQL. if we consider MySQL as the database. database vendors usually provide one or more industry−standard Application Programming Interfaces (API) for their product. This seems to hold true for just about every product on any platform. though.Chapter 13: Programming Interfaces
Overview
The most basic form of access for the majority of database users is through the tried−and−true command−line client tool. However familiar the end users become with the arcane commands and seemingly obscure tools that some of the database vendors have you use to get information into and out of their products. being compliant with a standard API in no way means that the database implements every function or method in the API. the most productive environments are the sole reserve of well−thought−out and implemented application programs. a third for JDBC (Java).

we discuss some basic ways to interact with databases. significantly speed up the database access portions of the application. The application doesnt directly use this detailed information. Upon successful connection (the login process completed successfully implying that the username parameter and the password parameter were correct) the application will have a valid (non−NULL) pointer to a data structure that represents the database session. This discussion is a general discussion of database connectivity and may vary depending on the unique situation. This preprocessing can.
322
. Stored Procedures Some APIs have special ways of executing and managing the results of stored procedures. we discuss what is necessary to connect to a typical database. This data structure holds detailed information necessary for subsequent database operations that occur during the same session. in some cases. The username and password have to have already been made known to the database security process by having been preassigned by a database administrator for that databasein other words.Basic Database Connectivity Concepts through an API
Before moving on to more specific examples of database connectivity. Next. SQL Statements The fundamental relational database operations that are needed when using a custom application are: • Create (Insert) new records • Update existing records • Read (Select) records • Delete existing records All significant application functions (as far as the database is concerned) must be implemented from one or more of these fundamental operations. so special handling of stored procedure results is often necessary. we present a brief discussion of some basic concepts. First. Statements that are candidates for being prepared are those that are executed frequently with little or no change to the statement. the machine location of the database. Prepared (SQL) Statements Several APIs can preprocess a SQL statement prior to the statement being executed.
Disconnecting from a database
Log out of the database using the same username that was used when logging into the database (implicitly used by way of the handle to the database). we discuss disconnecting from a typical database.
Connecting to a database
Basic database connectivity is achieved by supplying a database name. Stored procedures can implement several SQL statements within themselves. the user must already exist. and the name and password of a valid user (username parameter). finally. which frees the memory structure that was allocated for the connection. And.

Read the documentation carefully. Alternatively. 323
. DBI.Retrieving Metadata Metadata is information about data. MySQL C++.
ODBC and C/C++
The ODBC API goes back to the early 1990s when Microsoft implemented it from a preliminary specification for a CLI from X/Open and a similar specification from the SQL Access Group. CLI. the deletion of a single record from one table may be a transaction. and the PHP MySQL interface. or data about data. For a large number of database applications. Be aware that a specific database driver may be compliant with only a subset of the standard. this metadata is not used because the application knows ahead of time what to expect at each and every step of the way. the attribute (column) names of the tables. a transaction consists of all of the fundamental operations that must successfully complete as a unit. ODBC interfaces are implemented by a platform−specific driver manager and by database−specific drivers. So. for example. we use MySQL because it is widely available and supported on Linux and because it is open source software. metadata consists of information about the structures that make up the database. The most recent version of ODBC (currently in the 3. In database terms.
Table 13−1: Alphabetical List of ODBC Functions Function SQLAllocHandle( HandleType. The metadata is embedded in the application by design. connection. Although counterparts exist for practically all databases. However. C/C++ most often uses ODBC libraries. some vendors supply a CLI interface. However. the sizes and data types of the attributes. InputHandle.
API and Code Examples
This section lists the functions and provides examples for some of the more common APIs. then the transaction consists of all three update operations taken together. if a record in each of three different tables must either all be successfully updated together (three update operations) or none at all. if an application allows ad hoc access to the database. Transactions For multiple concurrent user databases (those of any interest) there is the concept of a transaction. For this chapter. Table 13−1 shows a list of ODBC functions. the two transaction operations are: • Commit a change to the database • Rollback a change to the database From the perspective of an end user. the relationships between the tables. supplied either by a third party or by the vendor of the database. the table names.x revision) is compliant with both the X/Open CAE Specification Data Management: SQL Call−Level Interface and ISO/IEC 9075−3:1995 (E) Call−Level Interface (SQL/CLI). The lists are complete lists of the functions for ODBC. one after another. it is mandatory that the application query for and examine the metadata for every result set in order to be able to present the data to the user without masking or otherwise obscuring the information contained therein. Description Obtains one of either an environment.

ValueMaxSize. *StrLen ) SQLGetDescRec( DescriptorHandle. *Value. Gets the cursor name associated with the specified statement handle. ColNumber. Handle. Attribute. *SQLStringInput. InformationValueMaxSize. *ValueSizeIndicator ) SQLGetDescField( DescriptorHandle.
Returns current values of some commonly used diagnostic information. information about supported data types for the current data source SQLMoreResults( StatementHandle ) Determines whether or not there are more result sets available and. (*Supported can point to a single value or to a list of values. *CursorName. as a data set. *ByteLenOfParam. RecordNum. Returns the value of a specified single descriptor field. Handle.
Gets the current value of a specific statement attribute (option). SQLDataType )
attribute (option). *ErrorMessage. SQLNumParams( StatementHandle. RecordNum. *Supported ) SQLGetInfo( ConnectionHandle. *Value. *StringOutputActualSize ) source for execution. InformationType. *Scale. RecordNum. ErrorMessageActualSize ) SQLGetEnvAttr( EnvironmentHandle. Returns the current value of a specific statement attribute. Attribute. *Value ) Used with SQLPutData to supply parameter data at query execution. Returns the text of an SQL statement as translated by StringInputLength. InformationValue. *Value ) SQLGetTypeInfo( StatementHandle. the driver and that will be presented to the data StringOutputMaxSize. C_DataType. *InformationValueSize ) SQLGetStmtAttr( StatementHandle. FieldIdentifier. *ParamName.) Returns information about the specified database driver and data source. Returns the value of a specified environment attribute. for example for bulk inserts. *SQLStringOutput. *Value. *ActualBytesWritten ) SQLGetFunctions( ConnectionHandle. *Precision. *ParamDataType. *IsNullable ) SQLGetDiagField( HandleType. Returns supported driver functions. *ActualValueSize ) SQLGetStmtOption( StatementHandle. statement. Returns the number of columns in the result set for *NumResultCols ) the statement handle. *Value. ValueMaxSize.
Returns additional diagnostic information (a single field of the diagnostic data structure). *ParamDataSubType. Returns part (for long datum) or all of one column of one row of a result set. Superseded 326
. *CursorNameActualSize ) SQLGetData( StatementHandle. Option. NameMaxSize. Function. *Value. RecordNum. ValueMaxSize. Returns the values of multiple descriptor fields. Returns the number of parameters in a prepared SQL *ParamMarkerNumber ) statement. ValueMaxSize. ErrorMessageMaxSize. SQLNativeSql( ConnectionHandle. Option. SQLNumResultCols( StatementHandle. Associates a set of bound parameter values with a SQLParamOptions( StatementHandle. Returns. *SQLStateValue. MaxSizeOfValue. *NativeErrorCode. See SQLPutData. CursorNameMaxSize. Identifier.SQLGetConnectOption( ConnectionHandle. initializes processing for the next result set. SQLParamData( StatementHandle. *NameActualSize. *ActualSizeOfValue ) SQLGetDiagRec( HandleType. *Value ) SQLGetCursorName( StatementHandle. if there are.

ValueSize ) Sets the current value of a specific statement SQLSetStmtOption( StatementHandle. SizeOrPrecision. Use SQLExecute to cause the query to actually run. *CursorName Names a cursor of a specified statement. SizeOfTableName. ValueLength ) specified value. Attribute. uniquely identifies a row in a specified table. *SQLQueryString. Associates a parameter in a SQL statement with C_DataType. variables in the calling application. *ProcName. refreshes data in OperationType. SQLSpecialColumns(StatementHandle. SizeOfProcSchemaName. *Value. SizeOfProcName. ProcCatNameSize. Value ) attribute (option). *Value. *ProcCatName. See SQLParamData. SQLSetConnectOption( ConnectionHandle. Sets the value of an environment attribute. *SchemaName. RowIdentifier Returns information about the set of columns that *CatName. SizeOfProcName. Sets the value of a statement attribute. ValueSize ) Sets values of multiple descriptor fields. SizeOfSchemaName. Scale. SQLSetStmtAttr( StatementHandle.NumberOfRows. ParamDataSubType. or delete. *Data. as well as the columns that make up the result set for the specified procedures. RecordNum. SizeOfColName ) SQLProcedures( StatementHandle. CursorNameSize ) SQLSetDescField( DescHandle. Option. Sets the value of the specified connection attribute Value ) (option).
Returns the list of procedure names that have been registered on a specific data source. *ProcSchemaName. QueryStringSize ) SQLPrimaryKeys( StatementHandle. Scale. Sets the specified connection attribute to the *Value. *ColName.
Returns the number of rows affected by an insert. Sends a query to a data source for preparation and later execution.
327
. SQLSetConnectAttr( ConnectionHandle. *TableName. SizeOfAttribute ) SQLSetParam( StatementHandle. *ProcName. *ValueSize ) SQLSetPos( StatementHandle. Positions a cursor within a row set. *SchemaName. ProcCatNameSize. Attribute. CatNameSize. *ProcSchemaName. Returns the list of input and output parameters. *Value. ByteLenOfParam. *CatName. Sets the value of a single descriptor field. SQL_DataType. RowNum. or updates or deletes data in an updatable result set. Option. Attribute. *ProcCatName. ParameterNum. *RowIndex ) SQLPrepare( StatementHandle. SQLSetCursorName( StatementHandle. update. ValueSize_Indicator ) SQLRowCount( StatementHandle. ParamDataType. ) SQLPutData( StatementHandle. *Value. ) SQLProcedureColumns( StatementHandle. CatNameSize.
Sends part (for very large datum) or all of a data value for a parameter. *Value. LockType ) the row set. RecordNum. Precision. RowCount )
in later versions. SizeOfProcSchemaName. *StrLen. Returns the list of column names that make up the primary key for a table. SQLSetDescRec( DescriptorHandle. *IsNull ) SQLSetEnvAttr( EnvironmentHandle. FieldIndentifier.

*SizeOfTableType ) SQLTransact( EnvironmentHandle. SizeOfTableName.
Table 13−2: Perl Documentation Notations and Conventions DBD DBI $dbh $sth $drh $h $rc $rv @ary $rows Meaning Static top−level class name Database handle object Statement handle object Driver handle object Any of the $dbh. *SchemaName. sends it to the database server for actual execution. or $drh handle types General Return Code (Boolean: true = OK. error checking/handling. specific data source. The DBI sends the method. SizeOfSchemaName. typically a row of data Number of rows processed 328
. *SchemaName. SizeOfTableName. IndexType.
Returns the list of table names (catalog) stored in a SQLTables( StatementHandle. *TableName. CatNameSize. and other duties. Superseded by SQLEndTran(). and the list of indexes associated with the table. SizeOfTableName. Table 13−2 and Table 13−3 illustrate these concepts. SizeOfSchemaName.
DBI and Perl
Perl applications use the Perl DBI interface module and one of the database drivers. CatNameSize. *CatName. RowIdentifierScope. The DBI is a database access module for the Perl Language. in turn. The module for a particular database is referred to as a DBD (database driver). *TableName. PagesAndCardinalityAccuracy ) SQLTablePrivileges( StatementHandle. It defines a set of methods. There are database interfaces for the specific databases available for Linux. ConnectionHandle. )
Returns statistics about a single table in a specified database. These drivers are implementations of the DBI methods written by using the private interface functions of the corresponding database server. and conventions that provide a consistent database interface independent of the actual database being used. CatNameSize. *SchemaName. *TableName. TableType. SizeOfSchemaName. *CatName. calls to the driver. false = error) General Return Value List of values returned from the database. Returns a list of tables and the privileges associated with each table in a specified database. *TableName. *CatName.SizeOfSchemaName. variables. $sth. which. The DBI is also responsible for the dynamic loading of database drivers. SizeOfTableName. Causes either a commit or rollback of all active Action ) transactions since the last commit. CanBeNullable ) SQLStatistics( StatementHandle.

If not already loaded. selectall_arrayref ($statement. $password)$dbh = DBI−>connect_cached ($data_source. @data_sources = DBI−> data_sources Returns a list of all data sources (databases) available via ($driver_name). The attributes are driver dependent. \%attr). and @row_ary = $dbh−> selectrow_array fetchrow_array into a single call. $ary_ref = $dbh−> to arrays for each row of data fetched. $dbh = DBI−>connect ($data_source. $password) Attempts to create a connection to the specified data_source and returns a database handle object if the $dbh = DBI−>connect_cached ($data_source. DBI−>trace($trace_level)DBI−>trace($trace_level. if needed. $username. In a list context. It should not be used for select statements because it does not return a statement handle. execute. or if the ping() method fails. @bind_values). To enable trace $trace_filename) information for a specific handle use the similar $h−>trace method described elsewhere. The attributes are driver dependent. Returns one of $dbh−>do($statement. be loaded.$rv = either the number of rows affected.@ driver_names = DBI−> available_drivers ($quiet). or This method is typically most useful for non−select statements that either cannot be prepared in advance (because of a limitation of the driver). Attempts to create a connection to the specified $auth. $rc = $dbh−>do($statement). \%attr. then a new connection is created.$rc = Prepare and execute a single statement. and fetchall_arrayref into a ($statement). this ($statement). are driver dependent. $ary_ref = $dbh−> selectall_arrayref Combines prepare. or which do not need to be executed repeatedly. the driver will data_sources ($driver. \%attr).
A file handle NULL values are represented by undefined values in Perl Reference to a hash of attribute values passed to methods
Description Returns a list of all available drivers by searching for DBD::* modules through the directories in @INC. Enables DBI trace information for all. \%attr) cached database handle has been disconnected.@row_ary = $dbh−> selectrow_array returns the first row of data from the statement. \%attr. not available. Efficiently combines prepare. $dbh = DBI−>connect data_source and returns a database handle object if the ($data_source. \%attr). −1 if not known or $dbh−>do($statement. If a previously $password.@ data_sources = DBI−> the named driver.$ary_ref = $dbh−> selectall_arrayref single call. By default. so you cant fetch any data. The database handle returned will be $username. returning a reference to an array of references ($statement. unless this behavior is inhibited by passing a true value for $quiet. a warning will be given if some drivers are hidden by others of the same name in earlier directories.$fh undef \%attr Table 13−3: Commonly Used Perl DBI Methods Method @driver_names = DBI−> available_drivers. stored in a hash associated with the given parameters for efficiency of further connection attempts. execute. @bind_values). \%attr). The attributes. The value of the DBI_DRIVER environment variable is the default if $driver is empty or undefined. In a 329
. connect succeeds. $username. connect succeeds. $username.

$rv = $sth−>bind_param ($p_num. ($p_num. $tbl_ary_ref = $sth−> fetchall_arrayref ($slice_hash_ref ). reference per row. this combines prepare. $ary_ref = $sth−> fetchrow_arrayref. Returns either undef (@bind_values) if an error occurs or true if successful regardless of the number of rows affected. the $bind_val variable is read when execute is called.
Similar to prepare except that the statement handle returned will be stored in a hash associated with the $dbh for efficiency of subsequent prepare calls using the same parameter values. Gets the next row of data as an array holding the field values. and fetch one column from all the rows of a result set. It returns a reference to an array that contains the values of the first column from each row. $rc = $sth−>bind_col ($col_num. As some drivers do not support placeholders. $rv = $sth−>rows.$ary_ref = The quickest way to retrieve data. \%attr) $sth = $dbh−> prepare_cached ($statement. $ary_ref = $dbh−> selectcol_arrayref ($statement.($statement. \%attr). \%attr)$rv = $sth−> bind_param_inout ($p_num. Typically a call to a stored procedure. @row_ary = $sth−> fetchrow_array. Retrieves. containing field name/field value pairs. vars_to_bind).$rv = $sth−>bind_param the prepared statement. @bind_values). Binds an output column of a select statement to a Perl user variable. all the data resulting from a prepared $tbl_ary_ref = $sth−> fetchall_arrayref and executed statement handle. \%attr)$sth = $dbh−> prepare_cached ($statement)$sth = $dbh−> prepare_cached ($statement. Use in conjunction with $sth−>bind_columns. $rc = $sth−>bind_columns (@list_of_refs_to_ Calls bind_col for each column of the select statement. ($slice_array_ref ). gets the next row of $sth−>fetch. Returns either the number of rows affected by the last 330
. \%attr). The bind_param method can bind (assign/associate) a $rv = $sth−>bind_param ($p_num. enables values to be output from. value with a placeholder. this returns the first field of the first row. $bind_value must be passed by reference. The parameter can be a previously prepared statement handle. $max_len)$rv = $sth−>bind_param_inout ($p_num. \%attr). \$col_variable). $bind_type). $bind_type) $rv = $sth−>execute $rv = $sth−>execute Executes the (prepared) statement. The $rc = $sth−>bind_param_inout ($p_num. $max_len. @bind_values). $bind_value.$statement @row_ary = $dbh−> selectrow_array ($statement. the statement. this method indicates that no more data will be fetched from this statement handle before it is either executed again or destroyed. $bind_value. data as a reference to an array holding the field values. or updated by. $rc = $sth−>finish. $hash_ref = $sth−> fetchrow_hashref. $allow_active)
scalar context. $hash_ref = Retrieves the next row of data as a reference to a hash $sth−> fetchrow_hashref ($name). execute. In a single call. $max_len. check the driver documentation carefully. as a reference to an array containing one $tbl_ary_ref = $sth−> fetchall_arrayref. indicated with a ? character in $bind_value). Prepares a single statement for subsequent later execution by the database engine. \%attr.$ary_ref = $dbh−> selectcol_arrayref ($statement. This returns a reference to a statement handle object. Good for housekeeping. \%attr. \$bind_value. The value in \$bind_value. \$bind_value. $ary_ref = $dbh−> selectcol_arrayref ($statement). \%attr. $sth = $dbh−> prepare($statement)$sth = $dbh−>prepare ($statement.

preparing a query. Upon successful connection (the login process completed successfully implying that the username parameter and the password parameter were correct) the application will have a valid (non−NULL) pointer to a data structure that represents the database session. Returns an error code in the standard SQLSTATE five−character format. perform transactions.$rc = $dbh−>commit. Perl DBI example:
$con1 = DBI−>connect ( $data−source−name. then free the memory structure that has been allocated for the connection.
$rc = $dbh−>rollback. $str = $h−>errstr. supply the name of a valid user (username parameter) and the correct password for that user to the database using DBI. $data_type).
Connecting to a database
The following example supplies a database name and the machine location of the database. Returns the native database engine error message from the most recent function. Disconnects the database from the database handle. $sql = $dbh−>quote($value. This data structure holds detailed information necessary for subsequent database operations that occur during the same session. executing the query and extracting and manipulating the metadata stored in attributes of the statement handle. Check the documentation to find out whether the target database supports transactions.
$rc = $h−>err.
Disconnecting from a database
Log out of the database using the same username that was used when logging in to the database (implicitly used by way of the handle to the data). Commits the most recent series of database changes since the last commit or rollback. Check the documentation to find out whether the target database supports transactions. Quotes a string literal for use as a literal value in a SQL statement by escaping any special characters (such as quotation marks) contained within the string and adding the required type of outer quotation marks. and disconnect from the database. or −1 if unknown or unavailable. The application doesnt directly use this detailed information. $login_name. 331
.
$rc = $dbh−>disconnect. We show how to connect to a database.
command that had an effect on any rows. Our example demonstrates connecting to a database. $rv = $h−>state.
Using the interface
We demonstrate some common uses of DBI with a simple mysql interface and wrap up DBI with an example of how to retrieve metadata using some of these features of DBI. Refer to the driver documentation for the exact values returned. retrieve results. Returns the native database engine error code (may be a string) from the last driver function called. Undoes the most recent series of database changes if the database supports transactions.
$sql = $dbh−>quote($value). The username and password have to have already been made known to the database security process by having been pre−assigned by a database administrator for that database. $login_password) || die $DBI::errstr.

# add any other application specific error handling code here } else { $dbh−>commit. It is run from the shell prompt and outputs the create table statement necessary to reproduce the table. So. in this case.Perl DBI example:
$con1−>disconnect || warn $dbh−>errstr. we use the same concepts to facilitate a more complex application in Chapter 16.
$stmt1 = $con1−>prepare ( q/Select name from Customer/ ) $rs = $stmt1−>execute. Although not so useful in itself. $statement1 can change prior to the eval.
Retrieving metadata
The following program illustrates connecting to a database and retrieving the metadata about a particular table. however. For example:
eval { $sth1=$dbh−>prepare($statement1) $sth2=$dbh−>prepare($statement2) $sth3=$dbh−>prepare($statement3) $sth4=$dbh−>prepare($statement4) $sth1−> execute $sth2−> execute $sth3−> execute $sth4−> execute }. the database rolls back.
Transactions
The documentation that comes with the Perl DBI module recommends using the eval{} method for transaction processing. Its purpose is to illustrate how some of the common DBI methods are used to manipulate data in a database.
Retrieving results
The following is how results are retrieved. If an error occurs. eval evaluates the statements within the block at runtime. }
The preceding code prepares several SQL statements and then executes them. when we reach this block it is executed (evaluated).
332
. if ($@) { # $@ contains $DBI::errstr if DBI RaiseError caused die $dbh−>rollback.
Updating rows
$sth = $dbh−>prepare($statement) $rc = $dbh−>do($statement)
Prepared (SQL) statements
$sth = $dbh−>prepare($statement) || die $dbh−>errstr. otherwise the statements are committed.

is the JDBC−ODBC bridge plus ODBC drivers. An object that represents a precompiled SQL statement. phone_number char(18).
Java and JDBC
The API for use with Java is JDBCJava Database Connectivity. premium_shipped char(20). The libararies come in four levels of compliance. The least−compliant level. It contains classes and interfaces for creating SQL statements. Comprehensive information about the database as a whole. This class of database drivers was initiated in order to get acceptance of Java for database applications off of the ground. The interface used to execute SQL stored procedures. JDBC Essential Package java. The interface used for the custom mapping of SQL user−defined types.
We see that the preceding perl program takes a customers name and returns the create statement necessary for creating the table. An object that can be used to find out about the types and properties of the columns in a ResultSet. and retrieving the results of executing those statements against relational databases.
Interface Array Blob CallableStatement Clob Connection DatabaseMetaData Driver PreparedStatement Ref ResultSet ResultSetMetaData SQLData SQLInput The mapping in the Java programming language for the SQL type ARRAY. The representation (mapping) in the Java programming language of an SQL BLOB.sql Provides the JDBC package. It consists of a set of classes and interfaces written in the Java programming language. JDBC has a framework in which different drivers can be installed dynamically to access different databases. JDBC provides a standard API for that makes it possible to write database applications using a pure Java API. The mapping in the JavaTM programming language for the SQL CLOB type. An input stream that contains a stream of values representing an instance of an SQL structured or distinct type.state char(20). ). The code uses the perl DBI functions access this information. JDBC is a standard API for executing SQL statements. A connection (session) with a specific database. The interface that every driver class must implement.
SQLOutput 335
. zip char(20). Java applications will use JDBC and one of the JDBC libraries for the particular database(s).0 A reference to an SQL structured type value in the database. A ResultSet provides access to a table of data. with level 4 being a native−protocol pure Java driver. JDBC is part of the standard Java distribution. Level 1. JDBC 2.

awt. import java.Date that enables JDBC to identify this as a SQL TIME value. It loads our specific database driver (in this case mm.mysql−2.applet.*. It then creates a drawing space. The object used for executing a static SQL statement and obtaining the results produced by it. This class is a thin wrapper around java.
336
. The basic service for managing a set of JDBC drivers. Next it connects to the database.Statement Struct Class Date DriverManager DriverPropertyInfo Time Timestamp Types Exception BatchUpdateException DataTruncation
The output stream for writing the attributes of a user−defined type back to the database. The class that defines constants that are used to identify generic SQL types. The standard mapping for an SQL structured type.*.
SQLException SQLWarning
An exception thrown when an error occurs during a batch update operation. it selects summary data about revenue and plots bar graphs on it.sql.
File PlotRevenue. Driver properties for making a connection. An exception that provides information on database access warnings.0. Finally.Applet. An exception that provides information on a database access error.1). A thin wrapper around java.Date that enables JDBC to identify this as a SQL TIMESTAMP value. It uses the Java try−catch syntax to catch errors along the way. import java.util.
Using JDBC
The following example takes advantage of Java graphics capabilities to generate a summary bar graph of the transactional data in our simple database.util.java : import java.
A thin wrapper around a millisecond value that enables JDBC to identify this as a SQL DATE. called JDBC types. An exception that reports a DataTruncation warning (on reads) or throws a DataTruncation exception (on writes) when JDBC unexpectedly truncates a data value. /* * The PlotRevenue program summarizes the data with a simple database * */ public class PlotRevenue extends Applet { /*************************** * initialize variables * ***************************/ public static int width=1000. public static int height=750.

mysql. Estimates based on numbers provided by NetCraft place PHP in use on more than 1 million sites around the world.com/) database servers (as shown in Table 13−4). avoiding any conflicts. and used it on his home page to keep track of who was browsing his rsum. the FI coming from an HTML form interpreter. MySQL support was added. Either PHP/FI or PHP3 ships with a number of commercial products such as C2s StrongHold Web server and Red Hat Linux. The product eventually evolved and the parser was rewritten from scratch. known as the Personal Home Page Tools. PHP will use the built−in MySQL client libraries. or auth mysql) should always specify the path to MySQL: −−with−mysql=/path/to/mysql.
Table 13−4: The MySQL Database API for PHP Database API mysql_affected_rows mysql_change_user mysql_close mysql_connect mysql_create_db mysql_data_seek mysql_db_query mysql_drop_db mysql_errno mysql_error mysql_fetch_array mysql_fetch_field mysql_fetch_object mysql_fetch_row mysql_field_flags mysql_field_name mysql_field_len mysql_field_seek Description Get number of affected rows in previous MySQL operation Change logged in user of the active connection Close MySQL connection Open a connection to a MySQL server Create a MySQL database Move internal result pointer Send a MySQL query Drop (delete) a MySQL database Returns the numerical value of the error message from previous MySQL operation Returns the text of the error message from previous MySQL operation Fetch a result row as an associative array Get column information from a result and return as an object Fetch a result row as an object Get a result row as an enumerated array Get the flags associated with the specified field in a result Get the name of the specified field in a result Return the length of the specified field Set result pointer to a specified field offset 339
. forming the basis for PHP Version 3. a number that compares favorably with Netscapes server product. Users who run other applications that use MySQL (for example. you must compile PHP with MySQL support by using the −−with−mysql option.PHP and MySQL
Rasmus Lerdorf developed PHP in 1994. consisted of a parser that only understood a few macros and a number of utilities implementing common home page features. such as counters and guest books. running PHP3 and PHP4 as concurrent Apache modules. and the package was renamed PHP/FI Version 2. The parser was rewritten in 1995. In order to have these functions available. This will force PHP to use the client libraries installed by MySQL. If you use this option without specifying the path to MySQL. MySQL functions allow you to access MySQL (www. The first public version.

sql
or
$SHELL_PROMPT> mysql N < batch_file_of_mysql_commands.
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. Implement your application to issue a connect request the least number of times possible You should use statement handles to manage multiple SQL statements instead of connecting and disconnecting several times to execute SQL statements. we offer some tips and concepts to help you steer clear of performance degradation. having a clear understanding of some basic concepts can avoid some pitfalls later on−and potentially a lot of tuning and rewriting.sql > batchfile. The following are some typical performance degradations and ways of avoiding them.mysql_field_table mysql_field_type mysql_free_result mysql_insert_id mysql_list_dbs mysql_list_fields mysql_list_tables mysql_num_fields mysql_num_rows mysql_pconnect mysql_query mysql_result mysql_select_db mysql_tablename
Get name of the table that the specified field is in Get the type of the specified field in a result Free result memory Get the id generated from the previous INSERT operation List databases available on a MySQL server List MySQL result fields List tables in a MySQL database Get number of fields in result Get number of rows in result Open a persistent connection to a MySQL Server Send a MySQL query Get result data Select a MySQL database Get table name of field
Linux Shell Scripts and Piping
Most Linux databases have a command−line interface that can also be used in Linux shell scripts. however. SQL statement objects provide access methods and data storage for SQL statements. a MySQL script may look like ( $SHELL_PROMPT> is the prompt for whatever OS platform is being used):
$SHELL_PROMPT >mysql −h <host> −u <user> p<password> −N < batch_file_of_mysql_commands. For example.
Some Notes about Performance
Finally. It is probably more typical to worry about performance issues when they arise. as the Perl DBI module provides an efficient cache for use with multiple connections to the same data source (refer to the description for DBI−>connect_cached in Perldoc). efficient connection management has an impact on application performance.sql select * from customers where last_update_date<=1999−12−31.out batch_file_of_mysql_commands. reusing one handle is still guaranteed to be the most efficient. Perl may be an exception to this.
Connecting to a data source
The process of connecting to a data source is expensive in terms of end−user time. The basic approach is to create an executable shell script having command lines in it that look identical to the same command as if it were entered interactively. So. However.

the ODBC API uses a different approach for determining. Therefore. in Perl DBI. itself returns a result set object. The application presumes that any changes have been successful. When a connection is initially made to a database. if there is no chance of corruption if a statement does not complete successfully. In these applications the combination of SQLPrepare and SQLExecute is dictated. that is. for order−entry applications.
341
. an application−managed data structure. and password. use SQLPrepare and SQLExecute for queries that are executed more than once. for better performance. transactions are at the statement level. at runtime. database recoverability is ensured. In transactional applications that use embedded SQL extensively.
Transactions and committing data
Committing data is I/O−intensive and. is slow. the application issues an explicit method or function to commit the changes. the driver can use the bound columns directly instead of going through an intermediate buffer.A common mistake is to issue multiple connect requests rather than the preferred (and probably intended) use of multiple SQL statement objects to the same database connection. autocommit on is the typical default mode. username. for example. SelectFrom queries.
Executing calls with SQLPrepare and SQLExecute versus direct execution
Certain ODBC. to optimize performance. For transaction processing in which multiple SQL statements must all complete as a unit or none complete at all. However. for example. and use SQLExecDirect for queries that are executed only once. turning autocommit off can improve performance because the I/O for a commit is not performed for every single SQL statement. To implement transactions across statements requires that the commit mode be set to manual. The reason to use column binding is that many database drivers are implemented to take advantage of binding result information directly from the data source into the user's buffer. that is. For example. the use of SQLPrepare and SQLExecute is intended for multiple executions of a statement that uses parameter markers. whereas the use of SQLExecDirect is intended for a single execution of a SQL statement. SQL queries that return result sets require the use of specific methods depending on the API.
Using column binding
Performance may also be improved by binding result set columns to application variables. and connecting and disconnecting repeatedly. it may be necessary to create multiple statement objects simultaneously using the same connection object in order to have the multiple SQL statements be able to commit or rollback the transaction as intended. This means that any changes to the database by each SQL statement are committed immediately upon successful completion of the statement without the explicit action of the application. For ODBC. Second. There are two implications to this: First. JDBC. instead of passing the database name. although it is possible to create query statements on the fly by using only string copy and string concatenation functions. This will reduce the number of method or function calls that the application will need to perform. For example. whether or not a query returned any results. the use of parameterized queries is widespread in order to implement data entry. applications that are designed as separate modules should pass the already established connection object pointer (or handle) between them. consequently. the method that is needed for queries that return results. and Perl DBI methods or functions are more efficient than others at executing queries depending on both the query type and how frequently it is used. Then.

Included are lists of the functions to these databases. In the remaining chapters in this part. we described APIs that are common to the UNIX environment. if the application is a Web application or a Linux desktop application.Summary
This chapter summarizes some APIs and interfaces that are common to a database on Linux MySQL. then using the ODBC driver is a good solution. we build applications using two of these interfaces. then some of the more modern APIs may be better suited for the task.
342
. We mentioned one very common API−ODBC−because of its pervasiveness in the industry. For the most part. It provides a few examples that use the API's basic functionality. If you are going to be accessing the database via a Windows machine. However. Which interface should be chosen is determined by the task at hand.

and for passing data between each driver and the application. uses the driver to establish a connection to a data source. These APIs included ODBC. JDBC.
Open Database Connectivity
As we noted in previous chapters. an archive of news articles. the driver manager loads the appropriate driver. The application can request that more than one driver be loaded into memory simultaneously. ODBC is available under Linux. To an application program. The driver receives statements from the application via the ODBC driver manager. we presented ODBC in the abstract. When the application closes the connection to that data source. and Perl API interfaces.Chapter 14: Programming APIs−Extended Examples
This is the second of two chapters on programming an interface to a relational database. JDBC. The ODBC standard defines a data source as being a repository of data plus the network interface used to access those data. This chapter discusses in greater detail how to code the ODBC. and PHP. the ODBC driver is invisible: the application never explicitly loads or frees a driver. • The ODBC driver is responsible for communicating with a data source. Rather. but it may be any source of data−for example. the programmer. but the fact is that ODBC is a truly open. translates each statement into the CLI expected by the data source. Commercial development of ODBC drivers has centered around the DOS/Windows for the same reason that Willie Sutton robbed banks−because 'that's where the money is. and returns a handle with which the application can work with the data source. write. and business logic. In the previous chapter. • The application code is what you. A repository of data usually is a relational database. This protocol provides a universal call−level interface through which applications can work with relational databases. To review quickly. Perl DBI. a consortium of software companies led by Microsoft Corporation designed the Open Database Connectivity (ODBC) protocol. and walk you through example program that work with MySQL. forwards the statements to the data source. • The driver manager is linked into the application. This chapter describes how to install and configure ODBC under Linux to access the MySQL database. the application tells the driver manager to open a connection to a data source. we presented synopses of a number of popular APIs with which you can work with a relational database. Washington.' However. SQL. and one or more drivers. and to let applications that are running under Linux access databases that are running under other operating systems. In the previous chapter.
Structure of an ODBC application
Chapter 12 presented the ODBC's architecture. Linux purists will look with skepticism at anything originating from Redmond. well−designed standard. the driver manager. It contains your user interfaces. The driver itself is implemented as a shared library that the driver manager loads into memory upon request. and walk you through how they work. with each driver being used to communicate with a different data source. We present a number of example programs.
343
. the driver manager drops the driver and frees the memory allocated for it. it is responsible for loading and unloading ODBC drivers. both to access databases that are running under Linux. an ODBC application has three parts: application code. As its name implies. and then receives replies from the data source that it returns to the application.

it is quite efficient. in fact. However. Type the command:
chmod +x install. although you may have another place you prefer.sh
344
. Because the drivers are implemented as shared libraries. for example. we describe how to install and configure an ODBC driver manager and an ODBC driver. We first describe the archives that must be downloaded and where they can be found.
Downloading archives
To load a precompiled version of iodbc onto your Linux system. and one of the Linux SDKs for your Linux system. In the following two subsections. two principal ODBC driver managers are available for Linux: • iodbc−This driver manager is maintained by OpenLink Corporation.
Installing software
After you have downloaded the archives. PostgreSQL. Much of the description is specific to the software that we use in these examples. It is based on an open−source driver manager written by programmer Ke Jin. It provides a GUI that a user can use to select ODBC drivers and define data sources that can be used by applications. glibc2. Create the directory in which you want the iodbc software stored. On this Web page's left frame. point your browser to the URL: http://www. When the SDK menu appears in the right frame. select the entry for the OpenLink iODBC software development kit (SDK) binaries. you should be able to use these descriptions as a template for installing and configuring the ODBC software that you wish to use with your application. however. We chose iodbc partly because we are familiar with it. and partly because its simplicity makes it easier to use. Move the archives into this file. as follows: 1. We suggest /var/iodbc. iodbc consists of a C library that is linked to an application.iodbc. we work with the iodbc driver manager. including MySQL. at least two ODBC driver managers are available for Linux. which is one of the first ODBC companies to support Linux. Enter the directory into which you are installing iodbc. this structure may seem overly complex.org/. select two entries: one for the generic installation script. and most commercial databases. su to the superuser root. Be sure to select the one compiled with the appropriate libraries. Installing a driver manager As of this writing.At first glance. • unixODBC−This driver manager attempts to reproduce the ODBC driver−management system used by Windows. and drivers are available for a number of databases. you're ready to install them.
Installing and configuring ODBC under Linux
ODBC is used mostly under Windows. you can add new drivers or update existing drivers without having to change your application at all−not even relink it. We then describe how to install the software and how to configure the software and your environment to use the software. The driver manager handles tasks that are common across all data sources. 3. 2. In this section. while the driver handles tasks for the data source.

In this example. However.com
When the page appears on your browser. which works with the C shell.csh. Execute these commands:
rmdir bin mv odbcsdk/*
This compensates for a bug in the installation script that causes it to build the wrong directory path into scripts openlink. scroll the right frame until you see MyODBC for UNIX.csh and openlink.sh or openlink. which works with the Bourne or bash shells. scroll the left frame until you see Downloads.mysql.36. That's all there is to it. or simply attempt to install and see if the rpm command complains of software mismatches.50.22. When the MyODBC download page appears.sh. otherwise.bash_profile. Type install. 4.23. Installing an ODBC driver This section presents examples that work with the MySQL database.bashrc instead of into $HOME/. however.0.23 works with server release 3. check the documentation that comes with the bits. the version may well have changed by the time you read this. Click the appropriate entry for the archive that you want. Type the command exit. to run MyODBC 2. and openlink. to cease having root permissions. if a copy of MyODBC is not included with your Linux release (and some do not include it). backs up previously installed iodbc software. For example.
Downloading archives
The first step is to obtain a copy of the ODBC driver. 6. In this example. If you want an installable archive of precompiled bits.csh (depending upon which shell you're running) into the configuration file for your shell. Then copy script openlink. It also builds two scripts with which you can set your environment for running iodbc: openlink. you should be able to use them as a template for installing an ODBC driver for your database of choice.sh.to make the installation script executable. however. If you are not sure whether the MyODBC bits you have downloaded work with your release of MySQL. click the entry for Binary RPM of MyODBC. MySQL provides an ODBC driver.sh to install the software. Fortunately. 5. which comes with MySQL 3. we work with the MyODBC driver. so we could avoid a more painful server upgrade.50. some key environmental variables (for example. that works with the MySQL database. 345
. we are running SuSE Linux 7. click it. called MyODBC. Now you are ready to install the ODBC driver. creates the directory odbcsdk. When the Downloads page appears. we use MyODBC 2. The descriptions in this section are tailored for MyODBC. point your browser to URL:
http://www.36. We describe how to download MyODBC and how to configure it. MySQL client 3. we had to upgrade the MySQL client software to release 3. scroll the right frame until you see MyODBC. be sure to copy it into file $HOME/.22 on its disks. so. LD_LIBRARY_PATH) will not be set properly. and dearchives the bits into subdirectory odbcsdk. This script dearchives the bits. If you are running bash. Note that you may have to upgrade your edition of MySQL to use the current distribution of MyODBC. click it.

and the port through which the database is accessed.ini.so localhost 3306 baseball /tmp/mysql. • Initialization is given in the form of a NAME=VALUE pairs. In this example. and then type the command:
rpm −i archivename
where archivename gives the name of the archive that you have just downloaded. however: to prepare an ODBC initialization file. The rpm manager will take care of installation for you. the next step is to install it. It installs the (somewhat sparse) documentation for MyODBC into directory /usr/doc/ packages/MyODBC. and then try again to install. the following adapts the example MyODBC initialization file to define a data source that accesses our baseball database:
[baseball] Driver = Server = Port = Database = Socket =
/usr/local/lib/libmyodbc. you will have to resolve them first. so set Host to localhost. and you have set your environment so that any applications you run will be able to find the shared libraries for the ODBC driver manager. This is quite simple: just su to the superuser root. the location of the driver to use. much as environmental variables are defined in your . but most packages base their initialization files on the Windows format. It also installs into /usr/doc/packages/MyODBC an example ODBC initialization file. called odbc. The only requirement is that the data source name be unique within the initialization file. but we did not have to do that. Each set of initializations is headed by a data source name (DSN).sock
• [baseball]−The data source name. In this example. Preparing the initialization file At this point. we have given the data source the same name as our database. With most ODBC packages. By default. which has the following structure: • The initialization file has the suffix . initialization information is passed through an initialization file. 346
. the application must pass a large amount of information to the ODBC driver manager. Before an application can connect with a data source via ODBC. you have installed both the ODBC driver manager and one or more ODBC drivers. • Host−The name or IP address of the machine upon which the database resides.profile file. • Driver−The path name for the shared library of the ODBC driver needed to connect to this data source. If rpm complains of any software mismatches. Each initialization set gives the information needed to connect to a given data source. • The initialization file can hold multiple sets of initializations. rpm installs the MyODBC driver into directory /usr/local/lib. it must tell the driver manager what database it wishes to open. Among other things. For example. The name and layout of this file vary from one ODBC package to another. One last step remains. which is given in square brackets.Installing the software
After you have downloaded the software. we discuss this file in the following section. the database is running on the same box that we are using.ini.

What these permissions are. The following gives the command line for compiling a simple ODBC program:
cc −s −o exeFile −I/var/iodbc/include srcFile. Option −s tells the C compiler to use shared libraries instead of statically linking a library into the executable. Finally. as you will see in the next section. the login identifier (as set on the remote system) of the user who is connecting with the data source. varies from one database package to another. Our application will pass those data to MySQL when we open the connection to the data source. one last preliminary task remains before we can write code: we must describe how to compile and link an ODBCapplication. we are finished with our preliminaries: we have installed and configured ODBC software. but we finally have our ODBC software installed and configured. Option −I/var/iodbc/include names the directory that holds the header files that came with the iodbc SDK. baseball. and that user's password. copy it into file . and we have compiled our ODBC programs. Note that this initialization file does not include some information needed to access the data source. After you have created the ODBC initialization file. and has appropriate permissions for manipulating the database. option −liodbc tells the linker to link library iodbc. and how to set them. • Port−The port through which the database is accessed. we look at the elements that appear in every ODBC application. then use the name of that directory instead. Option −L/var/iodbc/lib names the directory that holds the iodbc libraries that came with the iodbc SDK. if you install it elsewhere. if you install it elsewhere.c names the file of C code that we wish to compile. then name that directory instead. Compiling an ODBC application It has taken us a while to get this far. However. This assumes that the user has permission both to connect to the remote system.ini in your home directory. To begin our examination of ODBC. see the documentation for the database package with which you wish to work. −o exeFile names the executable that we wish to create. /var/iodbc is the directory into which we installed the iodbc SDK. When you have finished modifying the initialization file. • Socket−The socket file through which MySQL is accessed. we have prepared our initialization file. in particular. in this case. for details. we are ready to write some code. This is set to 3306. Now.odbc. As with the header files.• Database−The database with which you will be interacting. Remember that /var/iodbc is the directory into which we installed the iodbc SDK earlier in this section. which is the default port used by MySQL.
Basic program structure
Finally. which include:
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.c −L/var/iodbc/lib −liodbc
In this example.so into the executable that it builds. all you have to pass to the driver manager is the data source name. and srcFile. it does not hold the user's login or password.

SQLFreeEnv (henv). • When a program has finished working with a given data source.h. Free the statement handle. The names of the ODBC−specific header files may vary from one ODBC driver manager to another. whereas sqlext. it allocates and initializes the ODBC environment. These header files are included as part of the iodbc driver manager's development kit. }
When this program is compiled and run. printf ("Goodbye!\n").\n"). SQLFreeConnect (hdbc). • Each time it executes a SQL statement for a given data source. exit (EXIT_SUCCESS). Insert values into table "foo". SQLDisconnect (hdbc). Free the connection structure. Initialize the connection structure. Initialize the statement structure. Free the environment structure.h holds declarations that are specific to SQL.h−are standard C header files that are familiar to all C programmers. Three files−stdio. stdlib. • When a statement has finished processing. Allocation of resources At the risk of oversimplification. Disconnect from the data source. sql.\n"). Create table table "foo". and constants.h declare the ODBC−specific prototypes.h and sqlext. the program allocates resources for executing the statement. • Each time the program connects to a new data source. the program frees the resources set aside for that statement. types.h holds declarations that extend the SQL standard.h. Drop table "foo". Goodbye!
The following subsections describe each task that this program performs. printf ("Free the environment structure. it closes the connection with that 350
. it allocates and initializes the resources for communicating with that data source. you should see the following:
Initialize the environment structure.\n"). a program that uses ODBC consists of the allocation and freeing of resources: • When the program begins.printf ("Disconnect from the data source. printf ("Free the connection structure. and string. they reside in directory include under the directory into which we installed the development kit. Header files sql. For more information. Header files The beginning of the program declares five header files. check the documentation that comes with the driver manager that you are using.

a connection handle for the data source. and statement−the ODBC driver manager allocates resources and returns a handle: an environment handle for the environment. SWORD* complete_connect_string_length. as allocated by a call to SQLLAllocConnect(). To allocate resources for the ODBC environment. database connection. you are hell−bent on writing an application that is both buggy and nonportable.source and frees the resources used to communicate with it. SWORD complete_connect_string_max. data source. Connecting to a data source ODBC offers several functions with which a program can connect to a data source. SQLAllocConnect (henv. of course. UWORD completion_flag )
hdbc is the handle to the database connection. and a statement handle for the statement. and writes into variable henv the handle for the environment.
declare the variables that will hold the handles to our three sets of resources: environment. UCHAR* connect_string. HWND windowhandle. An ODBC application will only call this function once. using the appropriate manifest constant for each. The declarations
HENV HDBC HSTMT henv = SQL_NULL_HENV. or statement−unless. UCHAR* complete_connect_string. This call has the following syntax:
RETCODE SQLDriverConnect ( HDBC hdbc. as all ODBC connections share the same environment. Function RETCODE SQLAllocConnect (HENV henv. and HSTMT−is a typedef for a void*. which loads the appropriate ODBC driver and connects to the data source. The program then passes this handle to other ODBC calls. Our example programs use SQLDriverConnect(). • When the program has finished. We also initialized each to NULL. Each of the types−HENV. In Listing 14−1 we used these functions in the following calls:
SQLAllocEnv (&henv). HDBC. and exits. it frees the resources allocated for the environment. It writes into variable hdbc the handle of the data connection.
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. For each of these entities−environment. hstmt = SQL_NULL_HSTMT. hdbc = SQL_NULL_HDBC. Note that you can open an indefinite number of connections simultaneously (although our example program uses one).
Note that your application should not fool around with the internals of an environment. and statement. connection. SWORD connect_string_length. we call the following function:
RETCODE SQLAllocEnv (HENV* henv)
This function allocated the resources for the ODBC environment. &hdbc). HDBC* hdbc) allocates resources for a connection to a data source.

complete_connect_string_length points to a variable into which the ODBC driver can write the length of the text it has written into the buffer to which complete_connect_string points. Most Linux ODBC drivers do not use prompt boxes.PWD=mypassword". sizeof (buf). the ODBC driver manager uses this string to find the settings for the data source as defined in the user's ODBC initialization file. fail. connect_string_length gives the length of connect_string. 0. in effect. &buflen. Variable DSN names the data source. If you wish. This is strictly a Windows feature. contains all information needed to load the driver and connect to the data source). The user must confirm them before the driver will attempt to connect to the remote data source. It recognizes the following values: • SQL_DRIVER_PROMPT−Display a prompt box that shows the user the connection string values. SQL_NTS. completion_flag gives a flag that tells the driver what to do if the connection string is not complete.
Note the format of the third argument.windowhandle is a handle for a window that can be used to ask the user for the connection string. except that all fields that are not necessary to connecting to the data source are grayed out. the same as SQL_DRIVER_NOPROMPT. • SQL_DRIVER_COMPLETE_REQUIRED−The same as SQL_DRIVER_COMPLETE. this always should be zero. Type UCHAR is a typedef for unsigned char. This string consists of a set of variable=value pairs. The connection string must at least give the data source name and the password. In our program. Type SWORD is a typedef for short. and variable PWD sets the user's password. Finally. in bytes. or even override one or more settings that are in the user's ODBC initialization file. complete_connect_string gives the address of a place where the ODBC driver can write the complete connect string. the driver truncates it. connect_string gives the text of the connection string. which gives the connection string. The prompt box is displayed regardless of whether or not the connection string is complete (that is. Otherwise. of the array to which complete_connect_string points. in bytes. This buffer must be at least 255 bytes long.UID=mylogin. (UCHAR*) buf. which are separated by semicolons. SQL_DRIVER_COMPLETE). we invoked this function as follows:
rc = SQLDriverConnect (hdbc. The constant SQL_NTS indicates that connect_string is a C−style NUL−terminated string. complete_connect_string_max gives the length. As you can see. display a prompt box and ask for more information. that is. Variable UID gives the user identifier. you can also set other ODBC variables. then do so. "DSN=baseball. • SQL_DRIVER_COMPLETE−If the connect string contains all information needed to load the driver and connect. the connect string that has been "fleshed out" with definitions drawn from the initialization file. • SQL_DRIVER_NOPROMPT−If the connection string is not complete. under Linux. it consists of three variable=value pairs. just like the ODBC initialization file for the data source. so all four of these flags are. If the complete connection string is longer than the value given in complete_connect_string_max.
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.

For each database connection. error_message_maximum. 'in the background'−whereas others we can execute synchronously. and hstmt give the handles for. you can call function SQLError() to obtain further information. If a function returns SQL_ERROR or SQL_SUCCESS_WITH_INFO. respectively. Some we execute asynchronously−that is. • SQL_SUCCESS_WITH INFO−The call succeeded. the program should (under most circumstances) check this value before it proceeds to the next call. This value indicates if the called function succeeded. The application can request a detailed description of the error. The ODBC standard 353
. and the statement. but the driver wishes to give the application some extra information. error_message_actual)
henv. • SQL_STILL_EXECUTING−This value is returned if a statement is being executed asynchronously. • SQL_ERROR−An error occurred.Allocation of statement resources After we have connected to the database. and the application has requested information about its status. sql_state_string points to a character array into which SQLError() can write a string that describes the SQL state. a SELECT statement) returned no data. hdbc. hstmt. • SQL_INVALID_HANDLE−A call used an invalid handle. An ODBC call returns one of the following codes to indicate whether it succeeded: • SQL_SUCCESS−The call succeeded. error_message. This string is a four−digit number prefixed with one or more alphabetic characters. the ODBC environment. Handling errors As you probably noticed. HSTMT* hstmt)
hdbc gives the handle for the database connection that we obtained by calling SQLAllocConnect() and initialized through a call to SQLDriverConnect(). This function call has the following syntax:
RETCODE SQLError ( HENV HDBC HSTMT UCHAR* SDWORD* UCHAR* SWORD SWORD FAR* henv. call function SQLAllocStmt(). we can allocate multiple statements. Depending upon the nature of the error being checked. &hstmt). the data−source connection. In our program. we call it as follows:
SQLAllocStmt (hdbc. we can allocate resources for a SQL statement. each of the ODBC calls returns a value of type RETCODE. To do so. • SQL_NO_DATA_FOUND−Either a request for information (that is. Many calls return values in addition to these. as follows:
RETCODE SQLAllocStmt(HDBC hdbc. hstmt points to the variable into which the ODBC driver can write the handle for this newly allocated statement. sql_state_string. sql_native_error. hstmt or hdbc may be NULL. hdbc. or the application has retrieved all data.

connected to the database. This error code is specific to the data source. as set by a call to SQLAllocStmt(). error_message_maximum gives the length of this character array. and figured out how to handle errors. The constant SQL_NTS indicates that statement_text is a C−style NULL−terminated string. SDWORD is a typedef for long. in bytes. we use this call as follows:
rc = SQLExecDirect (hstmt. state_str. the message the driver wishes to write exceeds the memory your application has allocated to hold it−then SQLError() truncates the message so that it will fit into error_message. SQLExecDirect() takes the following syntax:
RETCODE SQLExecDirect ( HSTMT hstmt. for our first example.
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. to help you with debugging your program. "INSERT INTO foo(bar) VALUES (2)". SQL_NTS). sql_native_error points to a variable into which SQLError() can write the native error code. to trap errors and to print a diagnostic message should something go wrong. statement_text gives the address of the character array that holds the statement to be executed. error_message points to a character array into which SQLError() can write a string that describes the error. we can now do something with our database. &error_msg_len). "CREATE TABLE foo (bar INTEGER)". This function calls SQLError() as follows:
local_rc = SQLError (henv. rc = SQLExecDirect (hstmt. SDWORD statement_length)
hstmt gives the handle of the SQL statement. statement_length gives the length of statement_text. "INSERT INTO foo(bar) VALUES (1)". SQL_NTS). rc = SQLExecDirect (hstmt. Executing SQL statements Now that we have allocated resources. If this value exceeds that of error_message_maximum−that is. As you can imagine. We have written function check_return() to check the return value of each ODBC call. error_msg_avail.defines the errors that can be associated with any given ODBC call. error_message_actual points to a variable into which SQLError() writes the length of the message it wants to write into error_message. We explore these in our later examples. &native_error. UCHAR* statement_text. This function takes a SQL statement in the form of text. error_msg. hdbc. ODBC offers a wealth of calls for interacting with a database. hstmt. we look at the most elementary of these calls: SQLExecDirect(). and executes it directly upon the database. In Listing 14−1.
We call check_return() after practically every ODBC call. SQL_NTS).

The first call creates a table. we free the resources allocated to the ODBC environment by calling SQLFreeEnv(). To review. which has the following syntax:
RETCODE SQLFreeStmt (HSTMT hstmt)
where hstmt gives the statement handle. rc = SQLExecDirect (hstmt. we must close the connect and free resources. 355
. you have seen the framework for an ODBC program. Next. It has the following syntax:
RETCODE SQLFreeEnv (HENV henv)
where henv gives the environment handle. It has the following syntax:
RETCODE SQLDisconnect (HDBC hdbc)
where hdbc gives the data−source handle. Initializing the ODBC environment. we free the sources allocated to the data−source connection by calling SQLFreeConnect(). Free resources and disconnect After we have finished manipulating our database. The last drops table foo. SQL_NTS).rc = SQLExecDirect (hstmt. "INSERT INTO foo(bar) VALUES (3)". We do this in the opposite order from that in which we allocated and opened them. Listing 14−1 calls them as follows:
SQLFreeStmt (hstmt.
Each of these calls passes a string literal as statement_text. we call SQLDisconnect(). SQL_DROP). SQL_NTS). The next step is to disconnect from the data source. It has the following syntax:
RETCODE SQLFreeConnect (HDBC hdbc)
where hdbc gives the data−source handle. To do so. Our first task is to free the statement. "DROP TABLE foo". Initializing a data source and opening a connection to it.
Binding a variable to a parameter
At this point. The next three insert an integer into foo. we use the call SQLFreeStmt(). SQLDisconnect (hdbc). Finally. To do so. 2. SQLFreeEnv (henv). a program consists of these steps: 1. called foo. SQLFreeConnect (hdbc).

we can start doing some real work. hdbc. SQL_INTEGER. hstmt). Execute the statement. Listing 14−2 demonstrates how to prepare and execute a SQL statement. Checking return values for errors. bind. SQL_NTS).3. in most instances. This function has the following syntax:
RETCODE SQLPrepare ( HSTMT hstmt. henv. Freeing resources. SQL_C_SLONG. (UWORD) 1. rc = SQLExecute (hstmt). Initializing a statement. value++) { printf ("Insert value %d into table \"bar\". check_return (rc. we used function SQLPrepare() to prepare a statement. }
Prepare the statement To begin. Now that you have seen how to structure an ODBC program and how to use it to manipulate a data source. Prepare a SQL statement. The value of each variable within the SQL statement is read from its corresponding variable in your application. Under ODBC. SQL_PARAM_INPUT. value <= 3 . printf ("Bind a variable to the ? within the INSERT statement. henv. However. rc = SQLBindParameter (hstmt. hstmt).\n"). 4. Listing 14−1 calls function SQLExecDirect() to create a table and to populate it.\n"). for (value = 1 . hdbc. 0. hstmt). NULL). and execute a statement: Listing 14−2: Preparing a SQL Statement
printf ("PREPARE an INSERT statement. Each variable within the SQL statement is bound to a variable in your application 2. "INSERT INTO foo VALUES ( ? )". check_return (rc. check_return (rc. so we print here only the lines of code that illustrate how to prepare.
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. This is fine if you only wish to execute static SQL instructions. rc = SQLPrepare (hstmt. &value. 5. (UDWORD) 0. hdbc. value). which can be compiled directly into your program. building a SQL statement on the fly is a two−step process: 1. (SWORD) 0.\n". henv. 6. UCHAR* statement_text. and exiting. you will want to use variables to build SQL statements on the fly. Executing one or more instructions upon the data source. ODBC gives you a way to do this. Most of Listing 14−2 is a re−creation of Listing 14−1.

parameter_type flags the type of the parameter. as returned by a call to 476 SQLAllocStmt(). SWORD parameter_type.SDWORD statement_text_length)
hstmt is the handle of the statement we are preparing. we call the ODBC function SQLBindParameter(). SDWORD* parameter_length)
hstmt gives the handle for the statement being manipulated. SWORD column_scale. in bytes. SDWORD maximum_length. although this is not strictly necessary−Listing 14−10 demonstrates how to exchange data with a marker on the fly. The recognized C data types are: SQL_C_BINARY SQL_C_DOUBLE SQL_C_TIME SQL_C_TIMESTAMP SQL_C_CHAR SQL_C_SLONG 357 SQL_C_SSHORT SQL_C_USHORT SQL_C_DEFAULT
. SQL_NTS). In our example
rc = SQLPrepare (hstmt. • SQL_PARAM_OUTPUT−Data are being passed from the statement into the parameter. as they appear in the statement. C_data_type gives the type of the C variable that you are binding to the parameter marker. • SQL_PARAM_INPUT_OUTPUT−Data are being passed from the parameter into the statement. "INSERT INTO foo VALUES ( ? )". The ? markers are counted from left to right. UWORD marker_number. as follows: • SQL_PARAM_INPUT−Data are being passed from the parameter into the statement.
the statement contains one ?. Bind a variable to a marker To bind a variable to a parameter marker. UDWORD column_precision. The usual practice is to bind a variable to each marker. counting from one. SWORD C_data_type. It has the following syntax:
RETCODE SQLBindParameter( HSTMT hstmt. marker_number gives the number of the marker to which you are binding the parameter. PTR parameter_address. The handle must have been returned by a call to function SQLAllocStmt(). The constant SQL_NTS indicated that statement_text is a C−style NUL−terminated string. of statement_text. The question mark is a marker that tells SQLPrepare() that a variable will be used to pass data into or out of the statement at that point. then from the statement into the parameter. statement_text gives the text of the statement being prepared. statement_text_length gives the length. SWORD SQL_data_type.

these may vary from one driver manager to another. of the variable to which variable_address points. check the documentation that comes with the ODBC driver manager that you are using.h. SQL_PARAM_INPUT. SQL_C_SLONG. NULL). parameter_length gives the length in bytes of the buffer to which parameter_ address points.SQL_C_BIT SQL_C_ULONG SQL_C_STINYINT SQL_C_FLOAT SQL_C_DATE SQL_C_UTINYINT The iodbc driver manager declares these constants in header file sqlext. For details. 0. for example. The parameter is used only if its type is SQL_PARAM_INPUT or SQL_PARAM_INPUT_OUTPUT. read the header files themselves. (UDWORD) 0. column_precision gives the column's precision. Continuing with the discussion of the arguments passed to SQLBindParameter(). or if the documentation is minimal (as is the case with iodbc). SQL_INTEGER. parameter_length points to an array of SDWORDs. in this case.
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. each of which gives the size of one field within the structure. Other driver managers may declare them elsewhere. (SWORD) 0. Most are self−explanatory. Most are self−explanatory. we call SQLBindParameter() as follows:
rc = SQLBindParameter (hstmt. Again. parameter_address gives the address of the variable that is being bound to the parameter marker. check the driver manager's documentation for details. column_scale gives the column's scale. in bytes. It must be one of the following: SQL_BIGINT SQL_LONGVARBINARY SQL_NUMERIC SQL_FLOAT SQL_TIMESTAMP SQL_VARBINARY SQL_SMALLINT SQL_CHAR SQL_DECIMAL SQL_BINARY SQL_LONGVARCHAR SQL_REAL SQL_INTEGER SQL_TINYINT SQL_VARCHAR SQL_TIME SQL_DATE SQL_DOUBLE SQL_BIT The iodbc driver manager declares these constants in header file sql. (UWORD) 1. to pass data to a stored procedure. These constants may vary from one ODBC driver manager to another.h. This is a pointer rather than an integer because it is possible to bind a structure to a given parameter marker. &value.) For most common input variables. maximum_length gives the length. SQL_data_type gives the SQL data type of the parameter marker to which the variable is being bound. Data are being passed from the statement into the parameter. In our example. this can be set to NULL. (This is used.

say via an INSERT or UPDATE statement. This works well when passing data into a database. 1. henv. as we described earlier in this section. hstmt).
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. rc = SQLExecute (hstmt).\n\n". check_return (rc. check_return (rc. After this loop has finished executing. hstmt). as set by a call to function SQLAllocStmt(). henv. hdbc.\n"). as follows:
for (value = 1 . by binding a variable to a column. NULL).\n"). 0.\n"). henv. hdbc. called a cursor. value <= 3 . SQL_NTS). }
Each iteration of the loop inserts into the database the value that is written into variable value. In Listing 14−2. however. SQL_C_ULONG. rc = SQLCancel (hstmt). we call SQLExecute() within a loop. check_return (rc. ODBC also lets you read data directly from columns. you can move backwards or forwards within the cursor. value). and then returning it. The following subsections demonstrate both methods. printf ("\nThe maximum value in table \"bar\" is %d. Listing 14−3: Reading Data from a Cursor
rc = SQLExecDirect (hstmt. Most of this program repeats code given in Listing 14−1 and 14−2. parse the record. The following gives the code that demonstrates fetching data. value). printf ("Cancel further processing of the cursor. This function has the following syntax:
RETCODE SQLExecute(HSTMT hstmt)
hstmt is the handle of the statement.Execute the Statement Finally. hdbc. Reading data from a cursor Listing 14−3 demonstrates how to read data from a cursor. ODBC automatically creates a mechanism. rc = SQLGetData (hstmt.\n". In some instances. Listing 14−2 frees its resources and closes up shop. this mechanism does not address how to deal with SELECT statements. to reread records. &value. we call SQLExecute() to execute the prepared statement. hstmt). value++) { printf ("Insert value %d into table \"bar\". which do not use variables. and work with the data that the record contains. hstmt). check_return (rc. "SELECT max(bar) FROM foo". henv. hdbc. for managing the data that a SELECT statement returns. printf ("FETCH the output of the SELECT statement. Cursors let you read one record at a time.
Reading data returned by a SELECT statement
The previous subsection examined how to bind a variable to a ? parameter marker within a SQL statement. rc = SQLFetch (hstmt). printf ("Get the data returned by the FETCH statement.

We must call this function to close the cursor before we begin to close down our program. Note that you do not have to declare a cursor or execute it explicitly−ODBC automatically spools the output of a SELECT statement into a cursor. we call function SQLCancel() to abort further processing of the statement. Another way to handle close a cursor is to fetch data within a loop until SQLFetch() returns SQL_NO_DATA_FOUND. FETCH the output of the SELECT statement. This function was introduced in the previous subsection. Next.
When run. The maximum value in table "bar" is 3. marker_number. Cancel further processing of the cursor. Goodbye!
The first step is to call SQLExecDirect() to execute a SELECT statement. thus eliminating the need to call SQLCancel(). Finally. hstmt). Get the data returned by the FETCH statement. Note−no cursor declaration. After we have printed the value fetched from the database. The columns are identified in order. maximum_length. there are none). henv. it gives the number of the column from which data are being retrieved. This function has the following syntax:
RETCODE SQLFetch (HSTMT hstmt)
hstmt gives the handle for the statement in question. we call function SQLGetData() to move the fetched data into variables. Execute a SELECT statement. variable_address. The syntax of this function is:
RETCODE SQLCancel (HSTMT hstmt)
hstmt gives the handle for the statement in question. rather. We demonstrate this in Listing 14−5. hdbc. counting from one. This function has the following syntax:
RETCODE SQLGetData( HSTMT UWORD SWORD PTR SDWORD SDWORD*
hstmt. we call SQLFetch() to fetch a row that the SELECT statement selected from the database. from left to right. Blow away table "foo". at which point the ODBC driver then closes the cursor automatically. C_data_type. parameter_length)
These variables are the same as their counterparts in function SQLBindParameter().check_return (rc. This "drains" the cursor.
360
. Insert values into the table. this program prints the following:
Build a table. with one exception: parameter marker_number does not indicate a parameter marker within the statement (after all.

Cancel further processing of the cursor. 50. Goodbye!
First. 50. NULL). check_return (rc. team_str. variable_address. parameter_length)
These parameters are the same as for functions SQLGetData(). check_return(rc. Next. Listing 14−4 prints the following:
Execute a SELECT statement. hstmt). rc = SQLFetch (hstmt). Execute another SELECT statement. marker_number. hstmt). to execute a SQL SELECT statement.Bind a variable to a column Listing 14−4 demonstrates how to bind a variable to a column. team_str. SQL_C_CHAR. the program executes a call to SQLExecDirect().
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. Cancel further processing of the cursor. Bind a column to an integer variable. The team in Boston is the Red Sox.\n"). Note that in the call:
rc = SQLBindCol (hstmt. The syntax of this function is as follows:
RETCODE SQLBindCol ( HSTMT UWORD SWORD PTR SDWORD SDWORD*
hstmt. C_data_type.\n\n". FETCH the output of the SELECT statement. team_str). "SELECT team_name FROM team WHERE city = Boston'". rc = SQLCancel (hstmt). 1.\n").\n"). hdbc. NULL). FETCH the output of the SELECT statement. hdbc. rc = SQLBindCol (hstmt. printf ("Bind a column to a character variable. hstmt). Bind a column to a character variable. maximum_length. hdbc. check_return (rc. it calls function SQLBindCol() to bind a variable to one of the columns that is selected. printf ("Cancel further processing of the cursor. The relevant code is as follows: Listing 14−4: Binding a Variable to a Column
rc = SQLExecDirect (hstmt.
When compiled and run. SQL_C_CHAR. 1. printf ("FETCH the output of the SELECT statement. The table "team" has 26 rows. henv. henv. SQL_NTS). printf ("\nThe team in Boston is the %s. henv.

Cancel further processing of the cursor. Listing 14−5 demonstrates this. printf ("FETCH the output of the SELECT statement. which we trap and interpret. Bind a column to the output.\n"). NULL). hdbc. printf ("Bind a column to the output. The relevant code is as follows: Listing 14−5: Demonstrate SQL_NO_DATA_FOUND
printf ("Execute a SELECT statement that will fail.\n"). } else { printf ("\nThe team in Indianapolis is the %s. check_return (rc. hstmt). FETCH the output of the SELECT statement. hstmt). because Indianapolis does not have a major league baseball team. hdbc. Goodbye!
In this case. check_return (rc. The program then calls SQLFetch() as before. 1. the fetch automatically copies the data into the variable that is bound to the first column returned by the SELECT statement. henv. it prints the following:
Execute a SELECT statement that will fail. except that in this instance. henv. rc = SQLFetch (hstmt). "SELECT team_name FROM team " "WHERE city = Indianapolis'". and parameter maximum_length gives the number of bytes in the array. Again. If the SELECT statement contained erroneous code−for example. Indianapolis has no team. We do not have to call SQLGetData() to move data from the fetched row into the variable. SQL_NTS).\n\n". It also returns SQL_NO_DATA_FOUND if a SELECT statement returns no rows at all. SQLFetch() returns SQL_NO_DATA_FOUND upon its first invocation−as we expect. if (rc == SQL_NO_DATA_FOUND) { printf ("\nIndianapolis has no team. team_str. Error handling in a SELECT statement We mentioned earlier that the function SQLFetch() returns SQL_NO_DATA_FOUND to indicate that a cursor is empty. the program calls SQLCancel() to cancel further processing of the statement. }
When compiled and run.
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. 50.\n\n"). rc = SQLBindCol (hstmt. rc = SQLExecDirect (hstmt. team_str).\n"). a syntax error or requesting a nonexistent column−SQLExecDirect() will return an error code.parameter team_str points to a 50−character array. SQL_C_CHAR.

• Continue fetching until the FETCH statement indicates that the cursor is drained. rc = SQLBindCol (hstmt.\n\n"). printf ("Bind a column to the output. henv.\n"). while (1) { rc = SQLFetch (hstmt). we do not have to declare a cursor−ODBC builds one for us automatically. hstmt).
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. Goodbye!
We already introduced the functions SQLExecDirect(). henv. 1. team_str. SQLBindCol(). } }
When Listing 14−6 is compiled and run. hstmt). } else { printf ("%s. and the value it returns is checked to see whether the cursor is "drained. hdbc. it prints the following:
Execute a SELECT statement. SQL_NTS). if (rc == SQL_NO_DATA_FOUND) { break. FETCH the output of the SELECT statement. Listing 14−6 gives an example of how to do this. and SQLFetch(). SQL_C_CHAR. White Sox.\n". Bind a column to the output. NULL). their use in this code fragment should be clear by now." Again. regardless of the number of rows that the SELECT statement returns. check_return (rc. team_str). Cubs. hdbc. The only real difference from Listing 14−5 is that the function SQLFetch() is enclosed within a while loop. The relevant code is as follows: Listing 14−6: FETCHing
rc = SQLExecDirect (hstmt. 50. printf ("FETCH the output of the SELECT statement. you must do the following: • Execute a SELECT statement. • Fetch data that are spooled in a cursor. "SELECT team_name FROM team " "WHERE city = Chicago'". check_return(rc.Retrieving multiple rows from a SELECT statement To select multiple rows under ODBC.

hdbc. Cubs:−NO RECORD IN TABLE GAME' White Sox:−White Sox Goodbye!
In the above example. SQL_NTS). You can examine the flag. team_name. check_return (rc. NULL). rc = SQLBindCol (hstmt. printf ("Bind columns to the output. home_team. hstmt). FETCH the output of the SELECT statement. ODBC returns two variables for that column.team_name. check_return(rc. Bind columns to the output. 2. henv. henv. team_name. home_team). game. and then act appropriately. and the second holds a flag that indicates whether the column's value is NULL. any attempt to join table team to a record for a National League team in table team will return NULL.\n"). 20. we realize that because table game describes only games played by American League teams. } else { printf ("%s:−%s\n". The relevant code is as follows: Listing 14−7: Detecting and Handling NULL
rc = SQLExecDirect (hstmt. rc = SQLBindCol (hstmt. while (1) { rc = SQLFetch (hstmt).home_team " "FROM team " "LEFT JOIN game ON team. The first variable holds the value within the column.team_name = game. team_name). hdbc. this program prints the following:
Execute a SELECT statement. 20.home_team " "WHERE city = Chicago' " "ORDER BY team_name". } }
When compiled and run. } if (home_team_null == SQL_NULL_DATA) { printf ("%s:−NO RECORD IN TABLE GAME'\n".Handling NULL values NULL values present a problem for ODBC programs: that is. "SELECT DISTINCT team. Listing 14−7 demonstrates how to do this. if (rc == SQL_NO_DATA_FOUND) { break. SQL_C_CHAR. how do you represent a value that by definition is unrepresentable? The solution is straightforward: If a column can hold a NULL value. 1. hstmt). &home_team_null). SQL_C_CHAR.\n\n"). printf ("FETCH the output of the SELECT statement. 364
.

printf ("FETCH the output of the SELECT statement.
We could assign such variables for both fields. For example:
rc = SQLBindCol (hstmt. hstmt). 20. SQL_C_CHAR. number_rows++) { rc = SQLFetch (hstmt). henv. } sprintf (statement. "SELECT team_name FROM team WHERE city = %s'". .\n\n"). and then execute it. hdbc. for (number_rows = 0. (As you may have noticed. a long) as the last parameter in function SQLBindCol(). } else { printf ("%s. &home_team_null). 1. henv. NULL).
Handling user input
ODBC offers a number of ways to incorporate user input within a SQL statement.\n"). hstmt). To set a flag for a NULL−able field. 50. we must pass the address of a flag variable (a DWORD−that is. team_str. 2. we have to set a NULL flag for that column. check_return (rc. if (rc == SQL_NO_DATA_FOUND) { if (number_rows == 0) { printf ("No teams found. hstmt).\n"). printf ("Execute the statement. The most straightforward way is simply to build a string that holds the input.Thus. regardless of whether they are NULL−able. rc = SQLBindCol (hstmt.\n". t_city). SQL_NTS). home_team. rc = SQLExecDirect (hstmt. but it makes sense only to do so for the fields that are NULL−able−assuming that our program has that knowledge built into it. } } }
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. Listing 14−8 is an example of this. } break. statement. henv.\n"). The relevant lines of code are: Listing 14−8: User Input
while (1) { if (!get_city (t_city)) { break. team_str). hdbc. check_return (rc. printf ("Bind a column to the output. MySQL uses nonstandard syntax for declaring an outer join. our SELECT statement uses an outer join between tables team and game. Because column home_team may be set to NULL. check_return (rc. SQL_C_CHAR. hdbc.

rc = SQLBindCol (hstmt. hdbc. "SELECT count(*) FROM game". henv. if (rc == SQL_NO_DATA_FOUND) { break. ODBC also gives you the ability to set the default manner in which a data source handles transactions. • It calls SQLBindCol() to bind a variable to the one column in the SELECT statement. SQL_AUTOCOMMIT_OFF). However. hdbc. which is not shown here. 0. hstmt). Enter the name of the city (q' to quit): Indianapolis Execute the statement. rc = SQLExecDirect (hstmt. henv. rc = SQLSetConnectOption (hdbc. No teams found. check_return (rc. Cubs.The following gives an example session with this program:
Enter the name of the city (q' to quit): Chicago Execute the statement. White Sox. but to review briefly: • The program constructs a SELECT statement. and this points to some of ODBC's more powerful extensions. hstmt). • It calls SQLFetch() to read the rows in the cursor that the ODBC driver builds. check_return (rc. Bind a column to the output. passing user input to an ODBC program is relatively easy. Listing 14−9 shows how to execute a transaction with ODBC. the function exits. and should be familiar by now. hdbc. • It calls SQLExecDirect() to execute the statement. henv. and to return them one by one. while (1) { rc = SQLFetch (hstmt).\n"). Enter the name of the city (q' to quit): q Goodbye!
Function get_city(). FETCH the output of the SELECT statement. All of the ODBC calls have already been introduced. 1. As you can see. SQL_C_SLONG. FETCH the output of the SELECT statement. SQL_AUTOCOMMIT. } else
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. check_return (rc. SQL_NTS). If the user types q. uses the standard C functions printf() and gets() to accept input from the user. &number_rows. Bind a column to the output. NULL). hstmt).
Transactions
It is straightforward to commit or rollback a transaction under ODBC. The relevant portion of code is as follows: Listing 14−9: Executing a Transaction
printf ("Turn off autocommitting of data.

henv. number_rows). and again count them to ensure that they are gone. hstmt). henv. we: • Turn off autoexecution of transactions. hdbc. while (1) { rc = SQLFetch (hstmt). check_return (rc.{ printf ("Table \"games\" has %d rows. SQLTransact(). rc = SQLTransact (henv. UWORD transaction)
henv and hdbc. executes a transaction.\n". hdbc. rc = SQLExecDirect (hstmt. SQL_ROLLBACK). 0. HDBC hdbc. and SQLTransact(). } }
In this example. respectively. SQL_NTS). transaction is a flag that indicates the type of transaction to be performed. hstmt). hdbc. hstmt). and then count them one last time to ensure that the rows have reappeared. hstmt). • Count the rows in table game. if (rc == SQL_NO_DATA_FOUND) { break. } } printf ("Delete everything from table \"game\"\n"). NULL). UWORD is a typedef for unsigned short.
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. check_return (rc. • SQL_ROLLBACK−Roll back the transaction. "DELETE FROM game". printf ("Roll back the transaction\n"). rc = SQLExecDirect (hstmt. This example introduces two new ODBC calls: SQLSetConnectOption(). hdbc. check_return (rc. SQL_NTS). • Roll back the transaction. number_rows). "SELECT count(*) FROM game".\n". hdbc. check_return (rc. • DELETE every row from table game. 1. henv. so a statement's changes to the database will not be committed automatically. rc = SQLBindCol (hstmt. It must be one of the following constants: • SQL_COMMIT−Commit the transaction to the database. give the handles to the ODBC environment and the connection with which you are working. henv. SQL_C_SLONG. } else { printf ("Table \"games\" has %d rows. Its syntax is:
RETCODE SQLTransact ( HENV henv. &number_rows. as its name implies.

sql_buffer[0] = \0'.Databases and ODBC drivers vary as to whether they autocommit transactions. The nature of this parameter varies from one option to another−in some instances it is a flag. rolling back a transaction has no effect upon the contents of the database.
SQL interpreter
Our final ODBC example. for details. implements a generalized SQL interpreter. if (!strcmp(buffer.
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. "exit") || !strcmp(buffer. parameter is the value to which you are setting the constant. If they do autocommit data.h> #include "sql. The ODBC call SQLSetConnectOption() lets you set a default option for your connection. you can use this call to determine whether a database autocommits an SQL statement. set the option to SQL_AUTOCOMMIT and set the parameter to either SQL_AUTOCOMMIT_OFF or to SQL_AUTOCOMMIT_ON. see a reference book on ODBC. "Exit") || !strcmp(buffer. whereas in others. UDWORD parameter)
hdbc is the database connection whose option you are setting. then every SQL statement is committed to the database as soon as it is executed. option is a constant that identifies the option you are setting. fflush (stdout). char* semi_ptr.h> #include <stdlib. UDWORD is a typedef for unsigned long. "EXIT")) { return (0).h" #include "sqlext. respectively. it is a pointer or a file handle. while (1) { printf ("OK> ").h> #include <string. We show all of the source code for it: Listing 14−10: An ODBC−based SQL Interpreter
#include <stdio. The range of options that can be set with this call are too many to cover here. gets(buffer).h" /* −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− */ int get_statement( char* sql_buffer ) { char buffer[200]. Listing 14−10. UWORD option. To manipulate autocommitting. depending upon whether you want to turn autocommitting off or on. however. It has the following syntax:
RETCODE SQLSetConnectOption ( HDBC hdbc. In this instance.

It calls get_statement(). hdbc. NULL. hstmt). SQLFreeEnv (henv). function get_statement() uses some standard C library calls to retrieve the user's input. i. SQL_CHAR. The program calls SQLExecDirect() to execute the SQL statement. henv. which returns a SQL statement. hstmt). &precision. fetch_buffer. henv. The program then calls SQLNumResultsCols() to count the number of columns that is returned by the SQL statement just executed. SQLDisconnect (hdbc). and it should be familiar by now. check_return (rc. rc = SQLGetData (hstmt. team_name: White Sox team_name: Cubs OK> exit Goodbye!
To begin. exit (EXIT_SUCCESS). Function check_return() has not changed from our other example ODBC programs. &nullable). printf ("%s: ". &type. &null_indicator). } else { printf ("%s\n". We introduced this function earlier in this section. sizeof (fetch_buffer). after it has been compile